Preserve Thread Context by gRPC Interceptor

[aparajita31pandey]

Description

This change is build on top of #19005, where gRPC interceptor was introduced. It add ThreadContext to be accessed by the interceptors and also thread context preservation between interceptor and grpc Service execution

Problem: gRPC callbacks run on different threads than interceptors. OpenSearch's ThreadContext added by interceptor are in thread-local and gets lost during thread switches, when reaches gRPC ServiceImpl. In this diff,
After interceptors populate ThreadContext, we capture it using threadContext.newRestorableContext(false) and wrap all gRPC listener callbacks to restore the captured context before execution, following the same pattern as ContextPreservingActionListener

With this change, it bridges the gap between gRPC's async threading model and OpenSearch's thread-local context model.

Related Issues

Builds on #19005

Check List

Test Plan

• Functionality includes testing.

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❌ Gradle check result for 371161d: FAILURE

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❌ Gradle check result for ab49942: FAILURE

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❌ Gradle check result for 8356875: FAILURE

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[aparajita31pandey]

Flaky test - #15813

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✅ Gradle check result for 5859ce9: SUCCESS

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Codecov Report

❌ Patch coverage is 94.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.27%. Comparing base (b08de24) to head (5859ce9).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ansport/grpc/interceptor/GrpcInterceptorChain.java	90.47%	2 Missing ⚠️
...java/org/opensearch/transport/grpc/GrpcPlugin.java	96.29%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19776      +/-   ##
============================================
- Coverage     73.27%   73.27%   -0.01%     
+ Complexity    71641    71600      -41     
============================================
  Files          5785     5785              
  Lines        326935   326961      +26     
  Branches      47295    47296       +1     
============================================
- Hits         239576   239570       -6     
- Misses        68179    68193      +14     
- Partials      19180    19198      +18     

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