Building on support for setting feature flags by project, this adds
support for setting them by GitLab group path.
This is different from setting them by Flipper feature_groups, which
are for batch updating pre-registered collections.
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.
Previous code would not work with `disabled?` because that method would
send two parameters (second always `nil`) which we are not mocking.
Instead of mock yet another state, I decide to fix it where it belongs.
The GitHub importer (and probably other parts of our code) ends up
calling Feature.persisted? many times (via Gitaly). By storing this data
in RequestStore we can save ourselves _a lot_ of database queries.
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/39361
