[DRAFT] Introduce PluginMetadataClient

[fddattal]

Description

[Describe what this change achieves]

This PR introduces the PluginMetadataClient interface which abstractly exposes core metadata operations to plugins.

This pr is currently in draft. Tests are pending.

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Reference RFC: #13274

Check List

• [TODO] New functionality includes testing.
  • [TODO] All tests pass
• [Y] New functionality has been documented.
  • [Y] New functionality has javadoc added
• [N/A] API changes companion pull request created.
• [TODO] Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• [TODO] Commits are signed per the DCO using --signoff
• [TODO] Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• [TODO] 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 9d9e2dd: 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?

[dblock]

Looking at this code, is the SdkAwarePlugin additional abstraction really necessary? What's the reason that it's not called MetadataPlugin instead?

[opensearch-trigger-bot]

This PR is stalled because it has been open for 30 days with no activity.

[fddattal]

Update for posterity - We decided to move in another direction. More details on the RFC