chore: establish https://github.com/keyman-keyboards/khmer_angkor

[mcdurdin]

This is referenced in the kmc documentation and README files, so we need it for 17.0 launch

[mcdurdin]

See https://github.com/keyman-keyboards/khmer_angkor. Covers off what we need for 17.0 release.

This repo is very much a first baby step towards where we need to go. Specifically:

1. Github actions work but super rudimentary.
2. Release strategy incl. upload to keymanapp/keyboards needed.
3. Shared font strategy needed.
4. Development lifecycle documentation needed.

Lots of additional admin around the keyman-keyboards org required as well. We will quickly run into GitHub Actions usage limits (at least in free plan) if we move keyboards en-masse so let's work on this judiciously!