[Backport 2.x] Add ensureCustomSerialization to ensure that headers are serialized correctly with multiple transport hops (#4741)

[cwperks]

Manual backport of #4741 to 2.x

Resolves a conflict in the imports for ClusterInfoHolder between main and 2.x.

[codecov]

Codecov Report

Attention: Patch coverage is 86.20690% with 4 lines in your changes missing coverage. Please review.

Project coverage is 65.37%. Comparing base (ff7ac34) to head (80034cb).
Report is 5 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...arch/security/configuration/ClusterInfoHolder.java	60.00%	1 Missing and 1 partial ⚠️
...search/security/transport/SecurityInterceptor.java	86.66%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.x    #4743      +/-   ##
==========================================
+ Coverage   65.36%   65.37%   +0.01%     
==========================================
  Files         317      317              
  Lines       22158    22182      +24     
  Branches     3581     3584       +3     
==========================================
+ Hits        14483    14501      +18     
- Misses       5879     5881       +2     
- Partials     1796     1800       +4     

Files with missing lines	Coverage Δ
...org/opensearch/security/filter/SecurityFilter.java	65.87% <100.00%> (ø)
.../org/opensearch/security/support/Base64Helper.java	94.11% <100.00%> (+3.20%)	⬆️
...arch/security/configuration/ClusterInfoHolder.java	65.30% <60.00%> (-0.61%)	⬇️
...search/security/transport/SecurityInterceptor.java	80.68% <86.66%> (+0.91%)	⬆️

... and 3 files with indirect coverage changes