ZMK Versioning

[Nick-Munnich]

We want to add a proper versioning system to ZMK for multiple reasons:

• Nicer handling of external module ecosystem
• Stable branches prior to upgrading to Zephyr 3.7 (due to significant changes to how boards are defined)
• Putting users on stable versions rather than main which may suddenly break reduces help requests

Current decisions made are:

• Development work should happen in main
• When a new feature (or group of features) seems stable, create a new branch release
• Also create a new branch release prior to any breaking changes
• Released branches get some amount of bug fixes, goal is to keep them as stable as possible
• On bug fix, released branches get an additional tag added to them
• Releases are accompanied by some form of release notes, optionally an upgrading guide when needed
• New users are pointed to the latest stable branch when creating their config & setup

Unresolved questions that must be answered before beginning versioning are:

• What naming system should we use for released branches?

Unresolved questions that would be nice to answer before beginning versioning are:

• How do we handle versioning for the docs?

Unresolved questions that may best be answered afterwards are:

• What bugs should be fixed in released branches?
• Under what conditions should support for a released branch be dropped?
• Anything to do with LTS releases.
• Should we do any sort of "test/beta/stabilisation" release prior to a proper release?

Relevant discussion and content is here:

• Recent Discord discussion which lead to a bunch of decisions being made
• Timeline involving versioning
• Some initial discussion in the comments of feat(modularisation/docs) New hardware metadata version #2396
• A rejected attempt feat: Adding simple versioning using GHA to ZMK #2464
• Extra discussion
• Find current ZMK Version #1813 Towards a modular ZMK #453 are other affected issues

Other resources:

• Zephyr's versioning system described
• Samba versioning system was recommended as a read, as it uses a similar system

Please add any comments, thoughts, or questions, so that we can get this over with and get back to doing awesome stuff.