Implement support for Pulp manual createrepo

[FrostyX]

Fix #3498

[FrostyX]

I just wanted to push a proof of concept. This still needs to fix some quirks and refactor the code. Worth mentioning:

• This approach of having two separate repositories and "copying packages from one to another" was recommended by Dennis
• Currently we use fedora-rawhide-x86_64/devel/ directories on backend, but Pulp has a problem with that because the devel directory would encroach an existing repository. So that I used fedora-rawhide-x86_64_devel/ naming. I don't like it very much.

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[praiskup]

Have you considered to have two distributions, one for normal repo and one for the devel repo? https://pulpproject.org/pulpcore/docs/user/learn/lifecycle-promotion/

[Conan-Kudo]

What about fedora-rawhide-x86_64-staged/ instead?

[FrostyX]

Sorry for the delay, I finally updated the PR. It now uses two distributions (aka the "Lifecyle Promotion Support") instead of two repositories, as you've all suggested to do.

PTAL

[praiskup]

I'd prefer having a review session :-) on (post) today's meeting

[FrostyX]

Once again, this PR proves to be too complicated because I tested it once again while rebasing to main and found a bug.

[praiskup]

We should bump: https://github.com/fedora-copr/copr/blob/235810c90dfe47f59bde96d1cce2bb1cf32aa338/frontend/coprs_frontend/coprs/views/backend_ns/backend_general.py#L28

[praiskup]

:+1: for having the enum