Option that stops providing the *.repo files

[praiskup]

There are some reasons why the generate *.repo file is useless or at least
confusing

1. Some repositories stored in PULP may not be useful in isolation -
   rather they are used in "combination" (repo A is only useful when repo
   B is enabled, too). E.g. Copr has a few such use-cases, and therefore
   we sometimes provide a bit more complicated/combinded *.repo files

• the *.repo files might need some custom updates, example Allow to set gpgKey value for repository #2903

• external tooling (e.g. dnf copr enable, or the copr ansible plugin)
  might be responsible for generating a custom/arch specific *.repo files

This may lead to user frustration during attempting to consume the
PULP content through the default repo file generated by PULP. So it would
be nice to have a knob for not generating it at all.