Generate the gitlab's instance name from the api_baseurl by default
using the host of the given url.
This allows to create a lister task by simply specify the API base url and prevent 'inconsistent by default' behavior, eg. with:
swh-scheduler task add swh-lister-gitlab-full
api_baseurl=https://0xacab.org/api/v4
the created task does not use 'gitlab' as instance name (but '0xacab.org' here).
It's still possible to explicitely specify the instance name if needed.
depends on !46 (closed)
Migrated from D901 (view on Phabricator)