Add Gitweb lister

Depending on some instances, we have some specific heuristics, some instances:
- have summary pages which do not not list metadata_url (so some
  computation happens to list git:// origins which are cloneable)
- have summary page which reference metadata_url as a multiple comma separated urls
- lists relative urls of the repository so we need to join it with the main instance url
  to have a complete cloneable origins (or summary page)
- lists "down" http origins (cloning those won't work) so lists those as cloneable https
  ones (when the main url is behind https).

Refs. swh/devel/swh-lister#1800

setup.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-# Copyright (C) 2015-2020  The Software Heritage developers
+# Copyright (C) 2015-2023  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -69,6 +69,7 @@ setup(
         lister.gitea=swh.lister.gitea:register
         lister.github=swh.lister.github:register
         lister.gitlab=swh.lister.gitlab:register
+        lister.gitweb=swh.lister.gitweb:register
         lister.gnu=swh.lister.gnu:register
         lister.golang=swh.lister.golang:register
         lister.gogs=swh.lister.gogs:register