Add port order metadata to JACK sink / source ports

Add port order metadata to JACK sink / source ports

Adds JACK metadata property to ports created by *module-jack-sink*
and *module-jack-source* with key `JACK_METADATA_ORDER`, the port index
(1-based, in order of creation) as value and type
`http://www.w3.org/2001/XMLSchema#int`.

This allows JACK applications, which use JACK metadata, to list or display
these ports in correct order.

See also: https://jackaudio.org/api/group__Metadata.html

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>
Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/550>