Add doc and examples for auto-scaler and intializer (#1772)

* add doc and examples

* fix by lint

* revise the example

* revise init

* revise examples

* Update tidb-cluster.yaml

* revise by comment

* revise examples

* fix by lint

* address the comment

* Update examples/initialize/README.md

Co-Authored-By: DanielZhangQD <36026334+DanielZhangQD@users.noreply.github.com>

* Update examples/auto-scale/README.md

Co-Authored-By: DanielZhangQD <36026334+DanielZhangQD@users.noreply.github.com>

Co-authored-by: DanielZhangQD <36026334+DanielZhangQD@users.noreply.github.com>

examples/auto-scale/README.md

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+# Deploying TidbCluster with Auto-scaling
+
+> **Note:**
+>
+> This setup is for test or demo purpose only and **IS NOT** applicable for critical environment. Refer to the [Documents](https://pingcap.com/docs/stable/tidb-in-kubernetes/deploy/prerequisites/) for production setup.
+
+
+The following steps will create a TiDB cluster with monitoring and auto-scaler, the monitoring data is not persisted by default.
+
+**Prerequisites**: 
+- Has TiDB operator `v1.1.0-beta.2` or higher version installed. [Doc](https://pingcap.com/docs/stable/tidb-in-kubernetes/deploy/tidb-operator/)
+- Has default `StorageClass` configured, and there are enough PVs (by default, 6 PVs are required) of that storageClass:
+
+  This could be verified by the following command:
+
+  ```bash
+  > kubectl get storageclass
+  ```
+
+  The output is similar to this:
+
+  ```bash
+  NAME                 PROVISIONER               AGE
+  standard (default)   kubernetes.io/gce-pd      1d
+  gold                 kubernetes.io/gce-pd      1d
+  ```
+
+  Alternatively, you could specify the storageClass explicitly by modifying `tidb-cluster.yaml`.
+
+
+## Enabling Auto-scaling
+
+> **Note:**
+>
+> The Auto-scaling feature is still in alpha, you should enable this feature in TiDB Operator by setting values.yaml:
+ ```yaml
+features:
+  AutoScaling=true
+```
+
+Auto-scale the cluster based on CPU load
+```bash
+> kubectl -n <namespace> apply -f ./
+```
+
+## Destroy
+
+```bash
+> kubectl -n <namespace> delete -f ./
+```

examples/auto-scale/tidb-cluster-auto-scaler.yaml

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+apiVersion: pingcap.com/v1alpha1
+kind: TidbClusterAutoScaler
+metadata:
+  name: auto-scaling-demo
+spec:
+  cluster:
+    name: auto-scaling-demo
+  monitor:
+    name: auto-scaling-demo
+  tikv:
+    minReplicas: 3
+    maxReplicas: 4
+    metricsTimeDuration: "1m"
+    metrics:
+      - type: "Resource"
+        resource:
+          name: "cpu"
+          target:
+            type: "Utilization"
+            averageUtilization: 80
+  tidb:
+    minReplicas: 2
+    maxReplicas: 3
+    metricsTimeDuration: "1m"
+    metrics:
+      - type: "Resource"
+        resource:
+          name: "cpu"
+          target:
+            type: "Utilization"
+            averageUtilization: 80

examples/auto-scale/tidb-cluster.yaml

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+apiVersion: pingcap.com/v1alpha1
+kind: TidbCluster
+metadata:
+  name: auto-scaling-demo
+spec:
+  version: v3.0.8
+  timezone: UTC
+  pvReclaimPolicy: Delete
+  pd:
+    baseImage: pingcap/pd
+    replicas: 3
+    requests:
+      storage: "1Gi"
+    config: {}
+  tikv:
+    baseImage: pingcap/tikv
+    replicas: 3
+    requests:
+      storage: "1Gi"
+    config: {}
+  tidb:
+    baseImage: pingcap/tidb
+    replicas: 2
+    service:
+      type: ClusterIP
+    config: {}

examples/auto-scale/tidb-monitor.yaml

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+apiVersion: pingcap.com/v1alpha1
+kind: TidbMonitor
+metadata:
+  name: auto-scaling-demo
+spec:
+  clusters:
+  - name: auto-scaling-demo
+  prometheus:
+    baseImage: prom/prometheus
+    version: v2.11.1
+  grafana:
+    baseImage: grafana/grafana
+    version: 6.0.1
+  initializer:
+    baseImage: pingcap/tidb-monitor-initializer
+    version: v3.0.5
+  reloader:
+    baseImage: pingcap/tidb-monitor-reloader
+    version: v1.0.1
+  imagePullPolicy: IfNotPresent

examples/initialize/README.md

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+# Creating TidbCluster with Initialization
+
+> **Note:**
+>
+> This setup is for test or demo purpose only and **IS NOT** applicable for critical environment. Refer to the [Documents](https://pingcap.com/docs/stable/tidb-in-kubernetes/deploy/prerequisites/) for production setup.
+
+
+The following steps will create a TiDB cluster with Initialization.
+
+**Prerequisites**: 
+- Has TiDB operator `v1.1.0-beta.1` or higher version installed. [Doc](https://pingcap.com/docs/stable/tidb-in-kubernetes/deploy/tidb-operator/)
+- Has default `StorageClass` configured, and there are enough PVs (by default, 6 PVs are required) of that storageClass:
+
+  This could by verified by the following command:
+
+  ```bash
+  > kubectl get storageclass
+  ```
+
+  The output is similar to this:
+
+  ```bash
+  NAME                 PROVISIONER               AGE
+  standard (default)   kubernetes.io/gce-pd      1d
+  gold                 kubernetes.io/gce-pd      1d
+  ```
+
+  Alternatively, you could specify the storageClass explicitly by modifying `tidb-cluster.yaml`.
+
+
+## Initialize
+
+
+> **Note:**
+>
+> The Initialization should be done once the TiDB Cluster was created 
+
+The following commands is assumed to be executed in this directory.
+
+You can create the root user and set its password by creating secret and link it to the Initializer:
+
+```bash
+> kubectl create secret generic tidb-secret --from-literal=root=<root-password> --namespace=<namespace>
+```
+
+You can also create other users and set their password:
+```bash
+> kubectl create secret generic tidb-secret --from-literal=root=<root-password> --from-literal=developer=<developer-passowrd> --namespace=<namespace>
+```
+
+Initialize the cluster to create the users and create the database named `hello`:
+
+```bash
+> kubectl -n <namespace> apply -f ./
+```
+
+Wait for Initialize job done:
+```bash
+$ kubectl get pod -n <namespace>| grep initialize-demo-tidb-initializer
+initialize-demo-tidb-initializer-whzn7               0/1     Completed   0          57s
+```
+
+## Destroy
+
+```bash
+> kubectl -n <namespace> delete -f ./
+```

examples/initialize/tidb-cluster.yaml

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+apiVersion: pingcap.com/v1alpha1
+kind: TidbCluster
+metadata:
+  name: initialize-demo
+spec:
+  version: v3.0.8
+  timezone: UTC
+  pvReclaimPolicy: Delete
+  pd:
+    baseImage: pingcap/pd
+    replicas: 1
+    requests:
+      storage: "1Gi"
+    config: {}
+  tikv:
+    baseImage: pingcap/tikv
+    replicas: 1
+    requests:
+      storage: "1Gi"
+    config: {}
+  tidb:
+    baseImage: pingcap/tidb
+    replicas: 1
+    service:
+      type: ClusterIP
+    config: {}

examples/initialize/tidb-initializer.yaml

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+apiVersion: pingcap.com/v1alpha1
+kind: TidbInitializer
+metadata:
+  name: initialize-demo
+spec:
+  image: tnir/mysqlclient
+  imagePullPolicy: IfNotPresent
+  cluster:
+    name: initialize-demo
+  initSql: "create database hello;"
+  # initSqlConfigMap: tidb-initsql
+  passwordSecret: "tidb-secret"
+  # permitHost: 172.6.5.8
+  # resources:
+  #   limits:
+  #     cpu: 1000m
+  #     memory: 500Mi
+  #   requests:
+  #     cpu: 100m
+  #     memory: 50Mi
+  # timezone: "Asia/Shanghai"