ci: Fedora/EPEL/Arch builds in CI and OBS

The patchset moves downstream Fedora/EPEL spec file to upstream to enable us to test builds for these distros in upstream. This is currently used to:

• test Fedora/EPEL builds on every merge request in our own CI
• trigger Fedora/EPEL/Arch builds in OBS when new merge request is merged to master branch

There's one notable change in the version number for upstream tarballs. Pre-release versions like X.Y.Z-alpha or X.Y.Z-N-gFFFFFFF should only contain alphanumeric characters or dots (e.g. X.Y.Z.alpha or X.Y.Z.N.gFFFFFFF). This greatly simplifies packaging for Fedora/Arch, as these prerelease upstream version can be used in downsteam (where - character is banned in version number).

marked as a Work In Progress

changed the description

Also marking as WIP, so I don't forget to drop the last commit necessary for testing before we merge this.

Otherwise, the merge request should be working as is and is ready for review.

Sounds nice! (I just skimmed the code.)

changed title from WIP: ci: Fedora/EPEL builds in CI and OBS to WIP: ci: Fedora/EPEL/Arch builds in CI and OBS

changed the description

The OBS now also builds functional Debian / Ubuntu packages!