[Backport 2.x] Add canRemain method to TargetPoolAllocationDecider to move shards from local to remote pool for hot to warm tiering (#15010)

[neetikasinghal]

Description

Backports #15010

Check List

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

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[github-actions]

✅ Gradle check result for 201ae37: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.65%. Comparing base (9ba4c53) to head (201ae37).
Report is 2 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...rch/action/admin/indices/tiering/TieringUtils.java	80.00%	1 Missing ⚠️
...ting/allocation/allocator/LocalShardsBalancer.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##                2.x   #15628   +/-   ##
=========================================
  Coverage     71.64%   71.65%           
+ Complexity    64005    63986   -19     
=========================================
  Files          5243     5244    +1     
  Lines        299346   299367   +21     
  Branches      43570    43575    +5     
=========================================
+ Hits         214458   214502   +44     
+ Misses        66949    66944    -5     
+ Partials      17939    17921   -18     

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[opensearch-trigger-bot]

The backport to 2.17 failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-2.17 2.17
# Navigate to the new working tree
pushd ../.worktrees/backport-2.17
# Create a new branch
git switch --create backport/backport-15628-to-2.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 c760c3aeb9834c855462d0614358eb6f8c008549
# Push it to GitHub
git push --set-upstream origin backport/backport-15628-to-2.17
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.17

Then, create a pull request where the base branch is 2.17 and the compare/head branch is backport/backport-15628-to-2.17.