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

## Context

The `aws_mq` 2.0.0 release ([#20817](https://github.com/elastic/integrations/pull/20817)) 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/obs-infraobs-integrations — please create and maintain a `backport-1.x` (or equivalent) branch for `packages/aws_mq`, branched from the last 1.x tag, so future patches can be backported to the pre-9.6 audience.

## Related
- elastic/integrations#20817 (aws_mq 2.0.0 Identity Federation PR)

Start in packages/aws_mq and identify the last 1.x tag; review the branch-maintenance pattern in elastic/ingest-dev#8788 and the 2.0.0 context in integrations#20817. Create the backport-1.x or equivalent branch from that tag, and confirm it is available for future bug-fix and security backports to pre-9.6 stacks.

Written by the indexing model from the issue text.