Merge branch 'zj-move-repo-exists-opt-out' into 'master'

Repository Exists check is OPT_OUT for Gitaly

See merge request gitlab-org/gitlab-ce!15287

lib/gitlab/git/repository.rb

@@ -104,7 +104,7 @@ module Gitlab
       end
 
       def exists?
-        Gitlab::GitalyClient.migrate(:repository_exists) do |enabled|
+        Gitlab::GitalyClient.migrate(:repository_exists, status: Gitlab::GitalyClient::MigrationStatus::OPT_OUT) do |enabled|
           if enabled
             gitaly_repository_client.exists?
           else