Add back feature flag for cache invalidation
Part of #2288 (closed)
This adds back the feature flag for cache invalidation until the cache walker behavior defined in #2288 (closed) is corrected (see gitlab-com/gl-infra/production#1501 (comment 262058610) for more information on related incident).
This is essentially a partial revert of !1549 (merged).
Edited by GitLab Release Tools Bot