Guard new API with feature flag

ee/lib/api/merge_request_approvals.rb

@@ -54,6 +54,8 @@ module API
           hidden: true
         }
         get 'approval_settings' do
+          not_found! unless ::Feature.enabled?(:approval_rules, user_project)
+
           merge_request = find_merge_request_with_access(params[:merge_request_iid])
 
           present merge_request.approval_state, with: ::EE::API::Entities::MergeRequestApprovalRules, current_user: current_user

ee/lib/api/project_approval_rules.rb

@@ -3,6 +3,7 @@
 module API
   class ProjectApprovalRules < ::Grape::API
     before { authenticate! }
+    before { not_found! unless ::Feature.enabled?(:approval_rules, user_project) }
 
     ARRAY_COERCION_LAMBDA = ->(val) { val.empty? ? [] : Array.wrap(val) }