Refactor writable warm feature flag to include tiering

[neetikasinghal]

Description

Refactor the writable remote index feature flag to include the tiering functionality as well. Considered the following options:

1. TIERED_REMOTE_INDEX
2. TIERED_WRITEABLE_INDEX
3. TIERED_WRITEABLE_REMOTE_INDEX (Preferred)
4. TIERED_WRITEABLE_WARM_INDEX
5. TIERING_EXPERIMENTAL

Related Issues

Resolves #13718

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• API changes companion pull request created.
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• [] Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• [] Public documentation issue/PR created

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

❌ Gradle check result for c5a775e: 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?

[github-actions]

❌ Gradle check result for 6e9632c: 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?

[neetikasinghal]

❌ Gradle check result for 6e9632c: 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?

#13473

[github-actions]

❌ Gradle check result for 756e26a: 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?

[neetikasinghal]

❌ Gradle check result for 756e26a: 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?

#12197
#13600

[sohami]

❌ Gradle check result for 756e26a: 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?

#12197 #13600

Created tracking issue for other variants of failure as well: #13792

[github-actions]

❕ Gradle check result for 756e26a: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.52%. Comparing base (b15cb0c) to head (756e26a).
Report is 301 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #13719      +/-   ##
============================================
+ Coverage     71.42%   71.52%   +0.10%     
- Complexity    59978    61221    +1243     
============================================
  Files          4985     5062      +77     
  Lines        282275   287907    +5632     
  Branches      40946    41692     +746     
============================================
+ Hits         201603   205928    +4325     
- Misses        63999    64990     +991     
- Partials      16673    16989     +316     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sohami]

❕ Gradle check result for 756e26a: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

Created tracking issue for new flaky test: #13797. Other one is known: #13307

[opensearch-trigger-bot]

The backport to 2.x failed:

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

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-13719-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 da0cf847a3639b45efc34b211854284ecf00ef8d
# Push it to GitHub
git push --set-upstream origin backport/backport-13719-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-13719-to-2.x.