Move Pages directory in Sidekiq when renaming a project

This is behind the async_pages_move_project_rename feature flag. When it's enabled and a project is renamed, we do not move the Pages directory in Puma - instead, we schedule a Sidekiq job to perform the move.

We already weren't checking the return value of Gitlab::PagesTransfer#rename_project, so this shouldn't introduce any failure cases that weren't there already.

For #235802 (closed).