✨ Improve samples linting & fix samples lint issues

This commit includes:
- Fix linter issues
- Refactor fetchCronJob in sample controller reconcile func
- Fix simple-external-plugin-tutorial lint issues
- Fix getting-started tutorial lint issues
- Fix multiversion tutorial lint issues
- Fix cronjob-tutorial lint issues
- Refactor cronjob controller reconcile to reduce cyclomatic complexity

Author: wazery

.github/workflows/lint-sample.yml

@@ -16,7 +16,12 @@ jobs:
         folder: [
           "testdata/project-v4",
           "testdata/project-v4-with-plugins",
-          "testdata/project-v4-multigroup"
+          "testdata/project-v4-multigroup",
+          "docs/book/src/cronjob-tutorial/testdata/project",
+          "docs/book/src/getting-started/testdata/project",
+          "docs/book/src/multiversion-tutorial/testdata/project",
+          "docs/book/src/simple-external-plugin-tutorial/testdata/sampleexternalplugin/v1",
+          "docs/book/utils"
         ]
     if: (github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository)
     steps:

docs/book/src/simple-external-plugin-tutorial/testdata/sampleexternalplugin/v1/.golangci.yml

@@ -0,0 +1,47 @@
+run:
+  timeout: 5m
+  allow-parallel-runners: true
+
+issues:
+  # don't skip warning about doc comments
+  # don't exclude the default set of lint
+  exclude-use-default: false
+  # restore some of the defaults
+  # (fill in the rest as needed)
+  exclude-rules:
+    - path: "api/*"
+      linters:
+        - lll
+    - path: "internal/*"
+      linters:
+        - dupl
+        - lll
+linters:
+  disable-all: true
+  enable:
+    - dupl
+    - errcheck
+    - copyloopvar
+    - ginkgolinter
+    - goconst
+    - gocyclo
+    - gofmt
+    - goimports
+    - gosimple
+    - govet
+    - ineffassign
+    - lll
+    - misspell
+    - nakedret
+    - prealloc
+    - revive
+    - staticcheck
+    - typecheck
+    - unconvert
+    - unparam
+    - unused
+
+linters-settings:
+  revive:
+    rules:
+      - name: comment-spacings