[SPARK-33096][K8S] Use LinkedHashMap instead of Map for newlyCreatedE…

…xecutors

### What changes were proposed in this pull request?

This PR aims to use `LinkedHashMap` instead of `Map` for `newlyCreatedExecutors`.

### Why are the changes needed?

This makes log messages (INFO/DEBUG) more readable. This is helpful when `spark.kubernetes.allocation.batch.size` is large and especially when K8s dynamic allocation is used.

**BEFORE**
```
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 8 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 2 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 5 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 4 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 7 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 10 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 9 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 3 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 DEBUG ExecutorPodsAllocator: Executor with id 6 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:24:21 INFO ExecutorPodsAllocator: Deleting 9 excess pod requests (5,10,6,9,2,7,3,8,4).
```

**AFTER**
```
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 2 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 3 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 4 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 5 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 6 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 7 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 8 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 9 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 DEBUG ExecutorPodsAllocator: Executor with id 10 was not found in the Kubernetes cluster since it was created 0 milliseconds ago.
20/10/08 10:25:17 INFO ExecutorPodsAllocator: Deleting 9 excess pod requests (2,3,4,5,6,7,8,9,10).
```

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Pass the CI or `build/sbt -Pkubernetes "kubernetes/test"`

Closes #29979 from dongjoon-hyun/SPARK-K8S-LOG.

Authored-by: Dongjoon Hyun <dhyun@apple.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

resource-managers/kubernetes/core/src/main/scala/org/apache/spark/scheduler/cluster/k8s/ExecutorPodsAllocator.scala

@@ -67,7 +67,7 @@ private[spark] class ExecutorPodsAllocator(
 
   // Executor IDs that have been requested from Kubernetes but have not been detected in any
   // snapshot yet. Mapped to the timestamp when they were created.
-  private val newlyCreatedExecutors = mutable.Map.empty[Long, Long]
+  private val newlyCreatedExecutors = mutable.LinkedHashMap.empty[Long, Long]
 
   private val dynamicAllocationEnabled = Utils.isDynamicAllocationEnabled(conf)