bluez.lua: always hide sco-source nodes from applications

Since the loopback bluetooth source node is meant to be always used by applications, this change hides the actual bluez sco-source node by marking them as internal. This avoids showing 2 input devices in pavucontrol per BT device if HSP/HFP profile is enabled.

Beware that we need a version of pipewire with pipewire!1863 (merged) merged for this to work properly. If we don't have pipewire with that patch, it would not work properly as the loopback output stream expects to be linked with a sco-source node that has media class set to "Audio/Source/Internal".

Maybe we need to increase the minimum version of pipewire to 1.0.2?