Add some option to set manually group IDs of unicast streams
of devices.
Intel controllers don't appear to support more than one group at a time,
but in principle this can be done.
Fix some copypaste mistakes and other errors.
Add explanations for some more properties. Explain "drop-in" config
files. Explain filter-chain.conf.
Move configuration man pages under Configuration in TOC.
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.
Add pointer for readers to Wiki and WirePlumber docs, where the
documentation actually is at, so the configuration docs can found
starting from docs.pipewire.org
