Migrate CI / CD to GitHub Actions

As a Pillarbox developer I want a reliable CI orchestrated using GitHub Actions.

Acceptance criteria

All existing CI tasks can be run through GitHub Actions on self-hosted hardware.
Tasks perform in reasonable time.

[ ] Update scripts to be run with pkgx.
[ ] Create dedicated workflows.
[ ] Replace private configuration repository with GitHub secrets (p12 certificate and associated password, p8, other info).
[ ] Archive private configuration repository.
[ ] Setup microphone permissions on the agent if needed.
[ ] Cache things if possible (e.g. SPM).
[ ] Ensure steps fail correctly (e.g. if one test fails the test step must fail).
[ ] Optimize steps (e.g. use matrix to archive nightly / release in parallel).
[ ] Update developer documentation (in particular the required tool list after migration).
[ ] Optimize test suite (identify tests that take too long or reach the timeout, tweak timeouts, etc.).
[ ] Document CI setup, replacing the old Team City documentation.
[ ] ...