[SPARK-31946][CORE] Make worker/executor decommission signal configurable

[Ngone51]

What changes were proposed in this pull request?

This PR proposed to make worker/executor decommission signal configurable.

• Added confs: spark.worker.decommission.signal / spark.executor.decommission.signal
• Rename WorkerSigPWRReceived/ ExecutorSigPWRReceived to WorkerDecomSigReceived/ ExecutorDecomSigReceived

Why are the changes needed?

The current signal PWR can't work on macOS since it's not compliant with POSIX while macOS does. So the developers currently can't do end-to-end decommission test on their macOS environment.

Besides, the configuration becomes more flexible for users in case the default signal (PWR) gets conflicted with their own applications/environment.

Does this PR introduce any user-facing change?

No (it's a new API for 3.2)

How was this patch tested?

Manually tested.

[Ngone51]

cc @cloud-fan @dongjoon-hyun @holdenk Please take a look, thanks!

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/38103/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/38103/

[SparkQA]

Test build #133514 has finished for PR 30968 at commit 851d4c1.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[dongjoon-hyun]

+1, LGTM (except the naming comment).
Thank you, @Ngone51 .

[SparkQA]

Test build #133561 has finished for PR 30968 at commit 3afdf70.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/38150/

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/38150/

[dongjoon-hyun]

Merged to master for Apache Spark 3.2.0.