pattern: Use URL network location as instance name when not provided

Make the instance parameter of the base pattern lister optional and set lister name to URL network location when not provided.

It simplifies lister creation when associated forge type have a lot of instances in the wild (e.g. gitlab or cgit) while giving more details about the listed forge instance.

Also process listers for forge with multiple instances (cgit, gitea, gitlab, phabricator and tuleap) to ensure URL network location will be used when instance parameter is not provided.

Related to T3403

---

Migrated from D5989 (view on Phabricator)

swh/lister/cgit/lister.py

@@ -58,16 +58,12 @@ class CGitLister(StatelessLister[Repositories]):
         Args:
             url: main URL of the CGit instance, i.e. url of the index
                 of published git repositories on this instance.
-            instance: Name of cgit instance. Defaults to url's hostname
+            instance: Name of cgit instance. Defaults to url's network location
                 if unset.
             base_git_url: Optional base git url which allows the origin url
                 computations.
 
         """
-        if not instance:
-            instance = urlparse(url).hostname
-        assert instance is not None  # Make mypy happy
-
         super().__init__(
             scheduler=scheduler, url=url, instance=instance, credentials=credentials,
         )