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

## Context

The `aws_securityhub` 2.0.0 release ([#20529](https://github.com/elastic/integrations/pull/20529)) 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_securityhub`, branched from the last 1.x tag, so future patches can be backported to the pre-9.6 audience.

## Related
- elastic/integrations#20529 (aws_securityhub 2.0.0 Identity Federation PR)

Start by inspecting packages/aws_securityhub and the last 1.x tag, then compare the branch-maintenance pattern in elastic/ingest-dev#8788. Confirm the branch name and its relationship to the 2.0.0 work in #20529. Done means a maintained backport-1.x or agreed equivalent branch exists for pre-9.6 fixes and security patches.

Written by the indexing model from the issue text.