CI: improve nightly build workflow for the supported package types

[dciabrin]

Currently the nightly builds in CI use dedicated github repos for orchestrating the nightly rebuilds. The workflow is somewhat fragile and could be improve, e.g.:

• when a package type failed to rebuild, a tedious manual intervention is required to rekick the build, or patch the package metadata

• A single repository hosts metadata for all the four ngdevkit packages (emudbg, gngeo, ngdevkit-toolchain, ngdevkit), so triggering a rebuild currently involves a convoluted use of transient branches, which is not ideal

• Transient branches do not play nicely with azure CI and shields.io, so we can't easily add a shield to track the nightly build status of brew packages.

• The use of many transient branches require some additional garbage collection steps in CI to clean the package's git repo, which could probably be improved.

Workflow improvement

• deb rebuild workflow in Launchpad
• rpm rebuild workflow in COPR #95
• brew rebuild workflow in Azure DevOps #84
• Improve packaging on MSYS2 #87