Enable FF "reference_cache_memoization" by default

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/341849

Changelog: performance

config/feature_flags/development/reference_cache_memoization.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/341849
 milestone: '14.4'
 type: development
 group: group::source code
-default_enabled: false
+default_enabled: true