@jodumont yes. Samba is the only protocol on your list that is really made to be mounted locally. Personally I would try to avoid having to rely on php for access to remote filesystems (regardless of the protocol).
I agree with both of @girish's assessments of the file for the time being. But that doesn't mean that when Cloudron does support multi-site in the future, we can't assess multisite constants. So thanks for bringing it up! It lead me to that really interesting and eye-opening wp-config.php on Github.
@jodumont I think just having any recommended snippets in the docs would suffice for most, no? Then just copy/paste any you want to use using the File Manager (after making a backup in case it breaks something).