Cache any_project_with_shared_runners_enabled?

This change caches the any_project_with_shared_runners_enabled? method.

config/feature_flags/development/cache_shared_runners_enabled.yml

+---
+name: cache_shared_runners_enabled
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/68002
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/338267
+milestone: '14.2'
+type: development
+group: group::optimize
+default_enabled: false

ee/app/models/ee/namespace.rb

@@ -256,7 +256,13 @@ module EE
     end
 
     def any_project_with_shared_runners_enabled?
-      all_projects.with_shared_runners.any?
+      if ::Feature.enabled?(:cache_shared_runners_enabled, self, default_enabled: :yaml)
+        Rails.cache.fetch([self, :has_project_with_shared_runners_enabled], expires_in: 5.minutes) do
+          all_projects.with_shared_runners.any?
+        end
+      else
+        all_projects.with_shared_runners.any?
+      end
     end
 
     # These helper methods are required to not break the Namespace API.