The storage url is smb://user@server[:port]/share/path. The password can be
set in the environment variable DUPLICACY_SMB_PASSWORD for default storage or
DUPLICACY_<STORAGE_NAME>_SMB_PASSWORD.
This backend is based on https://github.com/hirochachacha/go-smb2. The
previous samba:// backend is just an alias for the disk-based backend with
caching enabled.
