Merge branch 'migration-status' into 'master'

Add option to specify migration status on at the migration site

See merge request !12976

lib/gitlab/gitaly_client.rb

@@ -86,8 +86,8 @@ module Gitlab
       feature.enabled?
     end
 
-    def self.migrate(feature)
-      is_enabled  = feature_enabled?(feature)
+    def self.migrate(feature, status: MigrationStatus::OPT_IN)
+      is_enabled  = feature_enabled?(feature, status: status)
       metric_name = feature.to_s
       metric_name += "_gitaly" if is_enabled