[Remote Store] Add support to restore only unassigned shards of an index (#8792)

[sachinpkale]

Backports c25c175 from #8792

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: FAILURE ❌
• URL: https://build.ci.opensearch.org/job/gradle-check/21215/
• CommitID: ab5b218
  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?

[sachinpkale]

Test is failing: org.opensearch.action.admin.cluster.node.tasks.ResourceAwareTasksTests.testBasicTaskResourceTracking.
Does not seem to be flaky. Checking

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      3 org.opensearch.search.SearchWeightedRoutingIT.testStrictWeightedRoutingWithCustomString

• URL: https://build.ci.opensearch.org/job/gradle-check/21219/
• CommitID: ab5b218
  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

Merging #8950 (b888607) into 2.x (5164fe2) will increase coverage by 0.14%.
Report is 1 commits behind head on 2.x.
The diff coverage is 38.88%.

@@             Coverage Diff              @@
##                2.x    #8950      +/-   ##
============================================
+ Coverage     70.64%   70.79%   +0.14%     
- Complexity    57265    57378     +113     
============================================
  Files          4745     4745              
  Lines        271070   271092      +22     
  Branches      39984    39988       +4     
============================================
+ Hits         191508   191929     +421     
+ Misses        63130    62719     -411     
- Partials      16432    16444      +12     

Files Changed	Coverage Δ
...on/admin/cluster/RestRestoreRemoteStoreAction.java	30.00% <0.00%> (-3.34%)	⬇️
.../java/org/opensearch/snapshots/RestoreService.java	52.80% <0.00%> (-1.01%)	⬇️
...remotestore/restore/RestoreRemoteStoreRequest.java	70.68% <100.00%> (+0.68%)	⬆️
.../opensearch/cluster/routing/IndexRoutingTable.java	76.22% <100.00%> (+0.19%)	⬆️
...a/org/opensearch/cluster/routing/RoutingTable.java	94.37% <100.00%> (ø)

... and 466 files with indirect coverage changes

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.index.ShardIndexingPressureSettingsIT.testShardIndexingPressureEnforcedEnabledDisabledSetting
      1 org.opensearch.index.ShardIndexingPressureSettingsIT.classMethod

• URL: https://build.ci.opensearch.org/job/gradle-check/21245/
• CommitID: b888607
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.