Use forge URL network location as default lister instance name

In order to simplify the mapping between a forge lister and the number of loaded origins after its execution (computed by swh-counters), a lister instance name should default to the network location of the listed forge URL.

For instance, below are the current gitlab lister instance names in production:

gitlab        | riseup
gitlab        | lip6
gitlab        | inria
gitlab        | freedesktop
gitlab        | ow2
gitlab        | common-lisp
gitlab        | gnome
gitlab        | gite.lirmm
gitlab        | gitlab
gitlab        | framagit

We would like to have the following instance names instead:

gitlab        | 0xacab.org
gitlab        | gitlab.lip6.fr
gitlab        | gitlab.inria.fr
gitlab        | gitlab.freedesktop.org
gitlab        | gitlab.ow2.org
gitlab        | gitlab.common-lisp.net
gitlab        | gitlab.gnome.org
gitlab        | gite.lirmm.fr
gitlab        | gitlab.com
gitlab        | framagit.org

Looking at swh-lister code, we could make the instance parameter optional and use the URL network location when not provided.

Looking at swh-scheduler code, if we change lister instance names, we will have to modify the values of the instance_name column for the listers table in production scheduler database (hopefully lister id is not computed from the instance name).

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Migrated from T3403 (view on Phabricator)