Enable branches API rate limit cache

Changelog: performance

config/feature_flags/development/api_caching_rate_limit_branches.yml

----
-name: api_caching_rate_limit_branches
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61688
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/330876
-milestone: '13.12'
-type: development
-group: group::source code
-default_enabled: true

lib/api/branches.rb

@@ -42,9 +42,7 @@ module API
         optional :page_token, type: String, desc: 'Name of branch to start the paginaition from'
       end
       get ':id/repository/branches', urgency: :low do
-        ff_enabled = Feature.enabled?(:api_caching_rate_limit_branches, user_project, default_enabled: :yaml)
-
-        cache_action_if(ff_enabled, [user_project, :branches, current_user, declared_params], expires_in: 30.seconds) do
+        cache_action([user_project, :branches, current_user, declared_params], expires_in: 30.seconds) do
           user_project.preload_protected_branches
 
           repository = user_project.repository