[RELEASE] Alignment with OpenSearch 3.0.0 GA

Context

The OpenSearch 3.0.0 GA release is currently scheduled for 2025/05/06: https://github.com/opensearch-project/opensearch-build/issues/3747
As such there will be desire for the clients to provide support for the 3.0.0 release.

Tasks

• Update integration test workflow matrices to include the released 3.0.0 (should also check 2.x version list is up-to-date)
• Update any integration tests against unreleased branches to include the 3.x branch
• Run the code generator (if any) against the latest specification changes
• If there are any breaking changes:
  • Check for any further low-hanging breaking changes/fixes worth bundling. (e.g. already deprecated workarounds/renames)
  • Document breaking changes in an UPGRADING.md file
  • Determine based on the level of changes if intermediary alpha/beta/RC releases may be required
  • Cut a new major version release
  • Create an issue (and/or raise a PR) on the documentation-website repository for updating the related client documentation
• If there are only non-breaking changes:
  • Cut a new minor version release
• Update the COMPATABILITY.md file to include OpenSearch 3.0.0 and any new client versions

Start by locating the integration test workflow matrices, integration tests for unreleased branches, and any code-generation entry point. Review the latest OpenSearch API specification changes, then update compatibility and release-related documentation as needed; done means OpenSearch 3.0.0 is covered, breaking or non-breaking changes are handled, and COMPATABILITY.md includes the new versions.