feat(90systemd-cryptsetup): socket key files

feat(90systemd-cryptsetup): socket key files

systemd v248 introduced support for using AF_UNIX stream sockets as key
files in /etc/crypttab. This commit enhances the 90systemd-cryptsetup
module to identify socket units with matching socket file paths.
It then includes the first matching socket unit along with its
corresponding service unit. This correspondence is determined by
checking the Service= option in the socket unit or, if that's not
available, by replacing the .socket suffix with either @.service or
.service, depending on the Accept= option (see systemd.socket(5)).

Futhermore, this functionality handles sockets located under
/run/cryptsetup-keys.d/, which are automatically discoverable by
the systemd-cryptsetup utility when the key file field in /etc/crypttab
is empty.