Ignore gitaly_ feature flags

gitaly_ feature flags are passed through to Gitaly
instead of being used in the Rails codebase.

When the feature flag is used only in E2E test
instead of rspec test, it would not be tracked
in 'tmp/feature_flags/*.used'.

scripts/used-feature-flags

@@ -39,6 +39,9 @@ flags_paths.each do |flags_path|
   Dir.glob(flags_path).each do |path|
     feature_flag_name = File.basename(path, '.yml')
 
+    # TODO: we need a better way of tracking use of Gitaly FF across Gitaly and GitLab
+    next if feature_flag_name.start_with?('gitaly_')
+
     all_flags[feature_flag_name] = File.exist?(File.join('tmp', 'feature_flags', feature_flag_name + '.used'))
   end
 end