Adopt Release Branch Strategy

[IfSentient]

Currently, the grafana-app-sdk releases from main and has commit-based tags. This prevents us from easily offering continued support for older releases. We should investigate moving toward release branches for each minor release (while still pre-1.0). To do so, we will need to ensure the following:

• The release script(s) work with release branches instead of main (either cutting a new one for a minor version bump, or using an existing one for a patch)
• PR's into release branches follow the same rules as PRs into main
• Dependabot can cut dependency upgrade PRs into active release branches as well as main (otherwise backporting dependency upgrades becomes higher-toil work)
• The release process needs better documentation