Increase default http.max_header_size to 16kb

[10000-ki]

Description

Our current default max header size is 8KB.

related osd issues

• [RFC] Improved session management security-dashboards-plugin#1311 (comment)
• [BUG] OpenSearch-Dashboards is slow to initialize as cookie sizes grow OpenSearch-Dashboards#9572

When using JWT token-based authentication, an 8KB header size is insufficient.
Elasticsearch encountered the same issue and has increased the default value to 16KB.
see : elastic/elasticsearch#88725

Unless there are any particular concerns, I suggest we do the same and change our default to 16KB as well.

Related Issues

Resolves #18022

Check List

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

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[jainankitk]

@10000-ki - Thanks for the code changes. Can you add changelog entry? Also, can you create a documentation issue for this change?

[10000-ki]

Thanks for the code changes. Can you add changelog entry? Also, can you create a documentation issue for this change?

@jainankitk yes sure i will add

[10000-ki]

@jainankitk hi~

i created a issue related doc : opensearch-project/documentation-website#9676

also

Once this PR is merged, I’ll try contributing to the documentation side as well.

[github-actions]

❌ Gradle check result for a77cceb: 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?

[jainankitk]

Unrelated test failure:

[Test Result](https://build.ci.opensearch.org/job/gradle-check/56834/testReport/) (1 failure / +1)

    [org.opensearch.snapshots.SharedClusterSnapshotRestoreIT.testSnapshotFileFailureDuringSnapshot](https://build.ci.opensearch.org/job/gradle-check/56834/testReport/junit/org.opensearch.snapshots/SharedClusterSnapshotRestoreIT/testSnapshotFileFailureDuringSnapshot/)

Retrying gradle check

[github-actions]

❌ Gradle check result for a77cceb: 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?

[10000-ki]

resolved conflicts

[github-actions]

✅ Gradle check result for 9bf6271: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.55%. Comparing base (52b8b05) to head (9bf6271).
Report is 18 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #18024      +/-   ##
============================================
+ Coverage     72.42%   72.55%   +0.13%     
- Complexity    67058    67136      +78     
============================================
  Files          5478     5478              
  Lines        310137   310130       -7     
  Branches      45087    45087              
============================================
+ Hits         224610   225016     +406     
+ Misses        67140    66795     -345     
+ Partials      18387    18319      -68     

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