Migrate project snippets to the ghost user when the user is deleted

At the moment, when a user is deleted, we migrate some records to the ghost user in order to keep the resources around.

Nevertheless, when the user is deleted, all their projects as deleted as well. We should migrate them to avoid deleting them

We have to make sure that, once the snippets are migrated to the ghost user, the snippets are still available to the project's users.