Add reference documentation for configuration settings & node/device
properties. We should have boring & exhaustive reference lists of all
the options, and an index where they can be looked up as needed.
The content is mostly stolen from the Wiki.
Add pipewire-client.conf.5, pipewire-jack.conf.5, and pipewire-device.7
that try to explain all available configuration settings for native/ALSA/JACK
clients, and parameters & properties devices.
Expand pipewire.conf.5 and pipewire-pulse.conf.5 with lists of supported
properties. Also explain environment variables.
Doxygen doesn't have an indexing mechanism suitable for configuration
settings, so add a simple one using an input filter and use it here.
Tweak styling a bit.
