Close RemoteStorePinnedTimestampService on Node.close()

[sachinpkale]

Description

• RemoteStorePinnedTimestampService internally manages an async scheduler.
• If not closed properly, integ tests sometimes fail with following exception:

com.carrotsearch.randomizedtesting.UncaughtExceptionError: Captured an uncaught exception in thread: Thread[id=6639, name=opensearch[node_t1][scheduler][T#1], state=RUNNABLE, group=TGRP-RemoteStorePinnedTimestampsGarbageCollectionIT]
	at __randomizedtesting.SeedInfo.seed([401E5CF6CD0D4727:9C0BCAD1CF20D2F6]:0)
Caused by: org.opensearch.core.concurrency.OpenSearchRejectedExecutionException: rejected execution of java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask@143262f2[Not completed, task = java.util.concurrent.Executors$RunnableAdapter@2866748[Wrapped task = org.opensearch.node.remotestore.RemoteStorePinnedTimestampService$AsyncUpdatePinnedTimestampTask@7794b6fc]] on org.opensearch.threadpool.Scheduler$SafeScheduledThreadPoolExecutor@16dc01db[Shutting down, pool size = 1, active threads = 1, queued tasks = 0, completed tasks = 124]
	at __randomizedtesting.SeedInfo.seed([401E5CF6CD0D4727]:0)

• Even though this does not have direct impact on live clusters as Node.close() closes threadpool, integ tests became flaky due to this.
• In this PR, we explicitly close RemoteStorePinnedTimestampService on Node.close()

Related Issues

• [AUTOCUT] Gradle Check Flaky Test Report for RemoteStorePinnedTimestampsGarbageCollectionIT #16088

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

✅ Gradle check result for 4940a0e: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.95%. Comparing base (a81b868) to head (4940a0e).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main   #16228   +/-   ##
=========================================
  Coverage     71.94%   71.95%           
- Complexity    64612    64633   +21     
=========================================
  Files          5298     5299    +1     
  Lines        301952   301965   +13     
  Branches      43627    43630    +3     
=========================================
+ Hits         217247   217267   +20     
+ Misses        66884    66828   -56     
- Partials      17821    17870   +49     

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