[aws_bedrock] The Path Forward: maintain 1.x branch for pre-9.6 stacks

## Context

The `aws_bedrock` 2.0.0 release ([#20822](https://github.com/elastic/integrations/pull/20822)) 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 2.x.

Following the pattern established in [elastic/ingest-dev#8788](https://github.com/elastic/ingest-dev/issues/8788), a maintained 1.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/security-service-integrations — please create and maintain a `backport-1.x` (or equivalent) branch for `packages/aws_bedrock`, branched from the last 1.x tag, so future patches can be backported to the pre-9.6 audience.

## Related
- elastic/integrations#20822 (aws_bedrock 2.0.0 Identity Federation PR)

Start with packages/aws_bedrock and the 2.0.0 change in integrations#20822; review the backport-branch pattern in elastic/ingest-dev#8788 and identify the last 1.x tag. Done means a maintained backport-1.x branch exists for pre-9.6 users and is ready to receive future bug and security patches.

Written by the indexing model from the issue text.