Review Database Queries for Feature Flags

Summary

Review database queries for Operations Feature Flags to see if they can be more performant.

See: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14515#note_190577605

Related Issue: https://gitlab.com/gitlab-org/gitlab-ee/issues/8240

Improvements

Risks

Involved components

Optional: Intended side effects

Optional: Missing test coverage