Missing workflows for distribution

[KaruroChori]

There are just minor adjustments to be added to the current CI pipeline:

• Add meson test run on current workflows
• Task to generate the full source distribution on release via meson
• Move flatpak generation to https://github.com/lazy-eggplant/vs.autobuilds
• Remove documentation for flatpak from here

Any other step currently reported @ releasing is manually handled for now.

Flatpak are going to be distributed as single file bundles: https://docs.flatpak.org/en/latest/single-file-bundles.html
At some point I might want to setup the repo for that, but today is not the day. no, we do

https://mesonbuild.com/Creating-releases.html

[KaruroChori]

I decided that all images/distributions which are not source and dockers will be handled externally.
So:

• debian
• arch packets
• flatpak
• brew
  All this will be in https://github.com/lazy-eggplant/vs.autobuilds

Docker I think would be better to stay here, as it is meant to support the development process. So, by accepting #21 and adding meson releases this task is done, and any delay in flatpak will be a concern of the other repo.