deskutils/xfce4-notifyd: Properly handle libcanberra dependency

xfce4-notifyd configure script automatically adds a dependency on
libcanberra-gtk3 if found on the system.

To have control on this I added a new CANBERRA option (disabled by
default) to the port to control configure behavior and ensure that
the port does not link to it if the option is disabled.

PR: 273805
MFH: 2023Q3