[RELEASE] Alignment with OpenSearch 3.0.0 GA

[Xtansia]

Context

The OpenSearch 3.0.0 GA release is currently scheduled for 2025/05/06: opensearch-project/opensearch-build#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

[OscarBarrett]

Is there a current plan for when work on this might be started?

And if anyone can confirm if the v2 client is working fine with OS3 when not using removed or changed features?