[aws_bedrock_agentcore] The Path Forward: maintain 0.x branch for pre-9.6 stacks

## Context

The `aws_bedrock_agentcore` 1.0.0 release ([#20821](https://github.com/elastic/integrations/pull/20821)) adds Identity Federation (Cloud Connectors) support via `var_groups`. This raises the minimum required Kibana and Elastic Agent versions to `^9.6.0`. Customers on 9.4.x–9.5.x stacks cannot upgrade to 1.x.

Following the pattern established in [elastic/ingest-dev#8788](https://github.com/elastic/ingest-dev/issues/8788), a maintained 0.x branch is needed so that bug fixes and security patches can be backported to users who cannot yet upgrade to 9.6.

## Ask

@elastic/obs-infraobs-integrations — please create and maintain a `backport-0.x` (or equivalent) branch for `packages/aws_bedrock_agentcore`, branched from the last 0.x tag, so future patches can be backported to the pre-9.6 audience.

## Related
- elastic/integrations#20821 (aws_bedrock_agentcore 1.0.0 Identity Federation PR)

Start with the packages/aws_bedrock_agentcore package and inspect the last 0.x tag, then compare the branching pattern in elastic/ingest-dev#8788 and the 1.0.0 change in integrations#20821. Done means a backport-0.x (or equivalent) branch exists from the final 0.x tag and is ready for future bug-fix and security backports.

Written by the indexing model from the issue text.