Draft: Allow `,` delimited list of gpgkeys
It is legal to have , delimted file paths for gpgkeys in a yum.conf
e.g
gpgkey=file:///foo/bar file:///bar/foogpgkey=file:///foo/bar, file:///bar/foo
are both legal.
Support both when copying the GPG keys into the correct location.
This wil still do the wrong thing if a ever a file path contains , but
so does DNF so that that's fine.