For features the feature gates are sometimes projects, not groups or
users. For example for git object pools:
https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/5872
This commit allows for setting feature group gates based on projects, by its
path as that seems most convenient.
Features could be listed and added through the api, now also removed.
This was needed in the case of gitlab.com as the number of gates that
were ever used just grows and cleaning up is hard.
This allows to enable/disable a feature flag for a given user, or a
given Flipper group (must be declared statically in the `flipper.rb`
initializer beforehand).
Signed-off-by: Rémy Coutable <remy@rymai.me>
