[Feature] prevent to add external library that contains a .immich file

I have searched the existing feature requests to make sure this is not a duplicate request.

• Yes

The feature

We should check for the presence of a .immich file, at least in the root directory and 1 directory deep, and prevent the user from adding an external library if a .immich file is found. This would decrease the number of people that break their install by creating recursive libraries.

Platform

• Server
• Web
• Mobile