Put Group MR analytics nav behind FF

The feature's navigation needs to be behind a FF as
the feature is still in development.

ee/app/helpers/ee/analytics/navbar_helper.rb

@@ -52,6 +52,7 @@ module EE
       end
 
       def group_merge_request_analytics_navbar_link(group, current_user)
+        return unless ::Gitlab::Analytics.group_merge_request_analytics_enabled?
         return unless group_sidebar_link?(:merge_request_analytics)
 
         navbar_sub_item(

ee/spec/features/groups/navbar_spec.rb

@@ -53,6 +53,16 @@ RSpec.describe 'Group navbar' do
     it_behaves_like 'verified navigation bar'
   end
 
+  context 'when merge request analytics is unavailable' do
+    before do
+      stub_feature_flags(group_merge_request_analytics: false)
+
+      visit group_path(group)
+    end
+
+    it_behaves_like 'verified navigation bar'
+  end
+
   context 'when value stream analytics is available' do
     before do
       stub_licensed_features(cycle_analytics_for_groups: true)