Fix NPE on restore searchable snapshot

[bugmakerrrrrr]

Description

Two changes here:

1. fix the issue in [BUG] Searchable snapshot restore - null_pointer_exception #12966;
2. make dynamic setting DATA_TO_FILE_CACHE_SIZE_RATIO_SETTING take effect.

Related Issues

Resolves #12966

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• API changes companion pull request created.
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[bugmakerrrrrr]

@andrross @kotwanikunal please help to take a look when you get a chance

[github-actions]

❌ Gradle check result for 60580f6: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[andrross]

Thanks @bugmakerrrrrr!

Let's add a changelog entry for this fix. Also it looks like there are spotless failures.

[github-actions]

❌ Gradle check result for f29bf75: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[andrross]

Looks like this failure might be related to this change?

REPRODUCE WITH: ./gradlew ':server:test' --tests "org.opensearch.cluster.routing.allocation.decider.DiskThresholdDeciderTests.testFileCacheRemoteShardsDecisions" -Dtests.seed=77C464051AC2A818 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=sr-Latn-ME -Dtests.timezone=Pacific/Guam -Druntime.java=21

org.opensearch.cluster.routing.allocation.decider.DiskThresholdDeciderTests > testFileCacheRemoteShardsDecisions FAILED
    java.lang.AssertionError: 
    Expected: <NO>
         but: was <YES>
        at __randomizedtesting.SeedInfo.seed([77C464051AC2A818:FE27C4DE8AE74CC9]:0)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
        at org.junit.Assert.assertThat(Assert.java:964)
        at org.junit.Assert.assertThat(Assert.java:930)
        at org.opensearch.cluster.routing.allocation.decider.DiskThresholdDeciderTests.testFileCacheRemoteShardsDecisions(DiskThresholdDeciderTests.java:462)

[github-actions]

❌ Gradle check result for f8b1083: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❕ Gradle check result for ed66558: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

Attention: Patch coverage is 82.14286% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 71.57%. Comparing base (b15cb0c) to head (ed66558).
Report is 330 commits behind head on main.

Files	Patch %	Lines
...uting/allocation/decider/DiskThresholdDecider.java	66.66%	1 Missing and 1 partial ⚠️
...es/settings/put/TransportUpdateSettingsAction.java	0.00%	1 Missing ⚠️
...g/opensearch/cluster/routing/OperationRouting.java	0.00%	0 Missing and 1 partial ⚠️
.../java/org/opensearch/snapshots/RestoreService.java	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #13911      +/-   ##
============================================
+ Coverage     71.42%   71.57%   +0.14%     
- Complexity    59978    61287    +1309     
============================================
  Files          4985     5065      +80     
  Lines        282275   288101    +5826     
  Branches      40946    41716     +770     
============================================
+ Hits         201603   206195    +4592     
- Misses        63999    64821     +822     
- Partials      16673    17085     +412     

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