external_ressources.py: add supported for GIT_URL in /config

[dalf]

The PR searx/searx#1900 brings support for searx branding.

The .../config URL adds some new fields:

• brand
  • GIT_URL
  • DOC_URL

GIT_URL should be use to check the vanilla status.

Internal to do:

• get_repository: the directory parameter becomes a parent directory. The real directory becomes some like os.path.join(directory, sha256(url)).
• GIT_URL must be ready when external_ressources.py runs.
• If the HTML column is neither V nor E, perhaps the instance doesn't comply with the AGPL license (see Bump pylint from 2.8.3 to 2.13.2 dalf/searx-instances#23 )

Extended version:

• add a new html page (a new tab) in the output to list different forks.

[dalf]

see

• [enh] HTML grade: check ressources according to static files in the fork git repository #70
• 5df9516
• 3eff4a9
• fdc695b