Fix cluster enviroment missing

See merge request gitlab-org/gitlab-ce!15973

(cherry picked from commit 888ed309)

9616e70a Allow environment_scope in cluster controllers
8a13ef41 Add environment scope field to cluster forms
56f719f8 Revert save button caption change
dd66c6a2 Use helper for feature check in cluster partials
2b45ae09 Hardcode clusters helper in CE
ecba48bd Inverse the has_multiple_clusters? helper usage