[Debian] Modernize debian release process

[bugwelle]

          In my company we use http://honk.sigxcpu.org/projects/git-buildpackage/manual-html/gbp.html and different branches for the different distributions.

Then the debianization is located only on the distribution branch. This mirrors the way Debian/Ubuntu are managing packages. As they use the software from upstream and put a debianization on top of it.

Originally posted by @iluminat23 in https://github.com/Komet/MediaElch/pull/1697#discussion_r1436893289