Enable caching on tags API

Changelog: performance

config/feature_flags/development/api_caching_tags.yml

----
-name: api_caching_tags
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/54975
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/324391
-milestone: '13.10'
-type: development
-group: group::source code
-default_enabled: false

lib/api/tags.rb

@@ -33,11 +33,7 @@ module API
 
         paginated_tags = Gitlab::Pagination::GitalyKeysetPager.new(self, user_project).paginate(tags_finder)
 
-        if Feature.enabled?(:api_caching_tags, user_project, type: :development)
-          present_cached paginated_tags, with: Entities::Tag, project: user_project, cache_context: -> (_tag) { user_project.cache_key }
-        else
-          present paginated_tags, with: Entities::Tag, project: user_project
-        end
+        present_cached paginated_tags, with: Entities::Tag, project: user_project, cache_context: -> (_tag) { user_project.cache_key }
 
       rescue Gitlab::Git::InvalidPageToken => e
         unprocessable_entity!(e.message)