[Backport 2.16] Add rest, transport layer changes for Hot to warm tiering - dedicated setup

[neetikasinghal]

Description

Backports #13980

Check List

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

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[github-actions]

✅ Gradle check result for 236a245: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 74.44444% with 69 lines in your changes missing coverage. Please review.

Project coverage is 71.52%. Comparing base (36dc24a) to head (236a245).

Files	Patch %	Lines
...ion/admin/indices/tiering/TieringIndexRequest.java	73.13%	10 Missing and 8 partials ⚠️
...earch/indices/tiering/TieringRequestValidator.java	78.04%	12 Missing and 6 partials ⚠️
...dmin/indices/tiering/HotToWarmTieringResponse.java	79.16%	9 Missing and 1 partial ⚠️
...n/admin/indices/tiering/RestWarmTieringAction.java	23.07%	10 Missing ⚠️
...admin/indices/tiering/TieringValidationResult.java	58.33%	9 Missing and 1 partial ⚠️
...dices/tiering/TransportHotToWarmTieringAction.java	85.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               2.16   #14890      +/-   ##
============================================
- Coverage     71.60%   71.52%   -0.09%     
+ Complexity    62565    62563       -2     
============================================
  Files          5110     5117       +7     
  Lines        293651   293920     +269     
  Branches      42791    42833      +42     
============================================
- Hits         210270   210212      -58     
- Misses        65755    66084     +329     
+ Partials      17626    17624       -2     

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