Make the update version automation run on schedule for all release branches

[rdner]

Describe the enhancement:
Currently, the "update versions" automation runs on a daily schedule:

https://github.com/elastic/elastic-agent/blob/0cdfef580e28e0488ae2bfa9e1372e083e3712c0/.github/workflows/bump-agent-versions.yml#L7C14-L7C23

Github allows to set a schedule only for the main branch. This means we have to manually run this automation for the rest of the release branches.

We should modify the script on main so it checks out all active release branches and runs the version updates for every branch creating corresponding PRs.

Describe a specific use case for the enhancement or feature:

Without this maintenance, the CI would start failing on release branches at some point and we would have to spend time on maintaining it manually.

What is the definition of done?

1. We have a daily Github workflow that runs version updates for each active release branch
2. We should have a way to configure what active release branches are, so we don't run this automation for branches we no longer release from.

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[v1v]

• We have a daily Github workflow that runs version updates for each active release branch
• We should have a way to configure what active release branches are, so we don't run this automation for branches we no longer release from.

There is already an implementation you can use for GitHub actions:

• https://github.com/elastic/oblt-actions/tree/main/elastic/active-branches

Or directly use https://storage.googleapis.com/artifacts-api/snapshots/branches.json - if you prefer or use Buildkite or something else.

---

NOTE: Only for Elastic employees:

There are a couple of backstage entries that explain those 'API' endpoints:

• https://backstage.elastic.dev/catalog/default/component/active-branches
• https://backstage.elastic.dev/catalog/default/component/current-releases

Let me know if you need further details

[rdner]

Thank you, @v1v !
I'll try it out and will get back to you if I have any questions.