Comps support for PULP repositories

[praiskup]

It seems people rely on this feature. See #4026

We should probably keep such projects on Backend for a while, see #3993.

[praiskup]

Brian asked instead of us here, PULP has support for comps uploads:
https://matrix.to/#/!NLyoXfybQSfvkVRUFB:matrix.org/$NWlapQcmhYnhBjQKVms-IungqAJXFwxJH93qP4NzPz0?via=matrix.org&via=ctrl-c.liu.se&via=fedora.im