[feature] add support for creating and serving yum/dnf repos

[aleiner]

Describe Proposed Solution(s):

Two possible approaches were discussed:

• When collecting RPMs of type 'repo', download and store in a temporary location. Once all of the RPMs have been gathered, run createrepo and then ingest that directory into the Hauler store. When the fileserver is serving files, this directory will be a valid yum/dnf repo.
• Collect all RPMs as and store directly into Hauler. Instead of doing a hauler store serve fileserver, run hauler store serve reposerver which will initiate the createrepo and launch an additional fileserver that will act as a valid yum/dnf repo.