Fix bug with delete shard routing weights on node restart

[imRishN]

Description

When a node is restarted after deleting the shard routing weights, the node fails to come up due to NPE encountered while reading WRR metadata. This PR fixes the bug

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)

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[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.search.backpressure.SearchBackpressureIT.testSearchTaskCancellationWithHighCpu
      1 org.opensearch.remotestore.SegmentReplicationUsingRemoteStoreIT.testDropPrimaryDuringReplication
      1 org.opensearch.cluster.allocation.AwarenessAllocationIT.testThreeZoneOneReplicaWithForceZoneValueAndLoadAwareness

• URL: https://build.ci.opensearch.org/job/gradle-check/17543/
• CommitID: aa11910
  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 #8057 (8daa8a5) into main (a81ef5a) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##               main    #8057      +/-   ##
============================================
- Coverage     70.92%   70.90%   -0.02%     
+ Complexity    56603    56571      -32     
============================================
  Files          4721     4721              
  Lines        267473   267473              
  Branches      39211    39211              
============================================
- Hits         189713   189661      -52     
- Misses        61767    61824      +57     
+ Partials      15993    15988       -5     

Impacted Files	Coverage Δ
...rg/opensearch/cluster/routing/WeightedRouting.java	65.51% <0.00%> (ø)

... and 477 files with indirect coverage changes

[github-actions]

Gradle Check (Jenkins) Run Completed with:

• RESULT: UNSTABLE ❕
• TEST FAILURES:

      1 org.opensearch.cluster.allocation.ClusterRerouteIT.testDelayWithALargeAmountOfShards

• URL: https://build.ci.opensearch.org/job/gradle-check/17544/
• CommitID: 8daa8a5
  Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.