- Added an ActiveSupport (using Rails.cache) caching adapter
- Overview of the new features can be found at https://johnnunemaker.com/flippin-features-at-runtime/
- Full Changelog can be found at https://github.com/jnunemaker/flipper/blob/v0.11.0/Changelog.md

Signed-off-by: Rémy Coutable <remy@rymai.me>

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

This is a follow-up for !12362 where this was documented but the code
was removed in the last iteration. Since this can still be useful and
this is already supported by the API, I think re-adding the code was
the best course of action.

Signed-off-by: Rémy Coutable <remy@rymai.me>

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>

This ensures we make maximum one call per feature per request.

See
https://github.com/jnunemaker/flipper/blob/v0.10.2/docs/Optimization.md#memoizing-middleware

Signed-off-by: Rémy Coutable <remy@rymai.me>

This is controlled with the feature flag gitlab_git_diff_size_limit_increase.
Both of these limits were basically picked arbitrarily in the first place;
disabling the feature flag reverts to the old limits.