Template folder should use the file id

[juliushaertl]

As per comment in #28645 (comment) the template folder should be stored using the file id of the folder instead of the path of a user which has the benefit that it would survive the rename or move of the folder itself.

I'd suggest to do a rolling upgrade of that part so that if we detect a path in the config, we switch it to the file id directly and continue to use that further on.

[Jerome-Herbinet]

I've moved my suggestions in a new issue (#33372).