Add automation for version bumps (patch releases only)

[bmorelli25]

Summary

This PR adds a workflow to automate the creation of a version bump PR for Elastic Stack patch releases.

Why

Patch releases make up approximately 79% of Elastic Stack releases and occur roughly once every two weeks. For the documentation release manager, the list of tasks includes, but is definitely not limited to:

• open an issue in elastic/dev
• open a PR in elastic/docs
• open a PR in elastic/docs.elastic.co
• full rebuild (going away with BuildKite builds)

I'd like to automate each of these steps. This PR is the first automation attempt.

How does it work

To open a version bump, a user simply needs to input the version that is being released and click "run". Within 30 seconds a PR will open.

Notes

This was tested in a private repo and works. We should double-check after this is merged to ensure that Elastic org perms don't break anything.

Next steps

• Add similar automation to elastic/docs.elastic.co https://github.com/elastic/docs.elastic.co/pull/200
• Automate issue creation (in progress)
• Single automation to trigger all three (PR, PR, issue) when managing a release (later)
• Add automation for minor releases (later)

[github-actions]

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[glitteringkatie]

LGTM!