Related to swh/meta#5075.

Some gitea origins can have non standard URLs in the form below:
(scheme)://(netloc)/(prefix)/(owner)/(project).

Previous loader implementation could not correctly compute API URLs
from such origin URLs so ensure it can.

Related to swh/infra/ci-cd/swh-charts#3.

This allows to drop one unneeded dependency on lister (which creates build issues
currently).

Refs. swh/infra/sysadm-environment#5017

It was noted while reviewing 786dcb82, but
I forgot to apply the change

journal_client: Tag 'get_origin_metadata' and 'metadata_fetchers' with forge type + Add metrics for the number of metadata items

The metadata-loader command was not available in that case as it was
not explicitly imported.

Use the proper entry point to register it in swh.core, and use the root
swh cli group in tests to make sure it's properly hooked up.

GitLab will display the content of the README file when browsing the
repository. But in case the file is a symlink, it will display the
path pointed by the symlink. There is a 6 year old issue about this:
https://gitlab.com/gitlab-org/gitlab/-/issues/15093

We can workaround the issue by having the content at the root of the
repository and a symlink to this file in the `docs/` directory.

Tested in swh/devel/swh-py-template!27

Related to swh/meta#4960

Related to swh/meta#4960

Related to swh/meta#4959

It will be used by the journal client to get the authority, so it can
check if we have recent metadata from that authority before fetching
it again.

There is no reason to expose it as it is only meant to allow
internal mocking

This fixes python 3.7 support due to poetry, a dependency of isort, that
removed support for that Python version in a recent release.

In order to remove warnings about /apidoc/*.rst files being included
multiple times in toc when building full swh documentation, prefer to
include module indices only when building standalone package documentation.

Also include them the proper sphinx way.

Related to T4496

- pre-commit from 4.1.0 to 4.3.0,
- codespell from 2.2.1 to 2.2.2,
- black from 22.3.0 to 22.10.0 and
- flake8 from 4.0.1 to 5.0.4. Also freeze flake8 dependencies.

Also change flake8's repo config to github (the gitlab mirror
being outdated).

This will allow the Git loader to incrementally load GitHub forks