Hi Guix!
This patch introduces a custom install phase for the gourmet variable,
because the combination of --root=/ and --prefix=/gnu/store/... will
lead to the generated paths in settings.py ending up with no preceding
slash. This means that the base dir in setting py is set to
'gnu/store/...gourmet...' instead of '/gnu/store/...gourmet...'.

This also adds another input to enable a plugin.

This is in response to guix #29227 and should fix the crash that is
observed.

Cheers, Mark

-- 
  Mark Meyer
  mark@ofosos.org