[SPARK-55725][K8S][DOCS] Make AbstractPodsAllocator docs up-to-date

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to make AbstractPodsAllocator documentation up-to-date:

• Use Javadoc style instead of Scaladoc according to the Apache Spark Code Style Guide.
• Add Since annotation for the class and methods.
• Update the class documentation with new DeploymentPodsAllocator.
• Update the method documentation with since tag.

Why are the changes needed?

AbstractPodsAllocator is one of DeveloperApi of the Apache Spark.

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

Lines 36 to 37 in 4da26e4

	@DeveloperApi
	abstract class AbstractPodsAllocator {

Recently, Apache Spark 4.2.0

• Added a new built-in implementation, DeploymentPodsAllocator.
  • [SPARK-54173][K8S] Add support for Deployment API on K8s #52867
• Added new API, setExecutorPodsLifecycleManager.
  • [SPARK-55075][K8S] Track executor pod creation errors with ExecutorFailureTracker #53840

Does this PR introduce any user-facing change?

No, this changes documentations only.

How was this patch tested?

Manual review.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Gemini 3.1 Pro (High) on Antigravity

[dongjoon-hyun]

Apache Spark uses Javadoc style instead of Scaladoc.

• https://spark.apache.org/contributing.html (Code Style Guide)

[dongjoon-hyun]

Thank you, @HyukjinKwon . Merged to master.