git-annex p2phttp should be able to serve multiple git repositories, eg all
the ones in a directory.

* Add a --directory option.
* When a request is received for a uuid that is not one it already knows
  about, it can rescan the directories to find new repositories that have
  been added.
* Removing a repository that it is serving should be ok, git-annex doesn't
  mkdir recursively down to the git repository level. So any running
  threads that are serving the removed repository will not recreate it,
  and will fail out.
* Removing a repository and then re-creating it with a different UUID
  though would be problimatic and probably the documentation would need to
  say to not do that, restart git-annex p2phttp after deletion in that
  case.

I asked matrss if this would be useful for forgejo-aneksajo and he said
"Serving more than one repository per p2phttp instance would probably be
very useful, although I think I can work with the limitation [of only 1]."

[[!tag projects/INM7]]