module-jack-sink/source: 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 #1197 (closed)).

Errors setting the port metadata are logged and ignored, since older JACK versions (e.g. jack2 < 1.913) do not implement metadata (but they still have the metadata API functions).

This implementation also restricts the size of the string holding the integer port index to 3 (plus \0), so port indexes > 999, will get truncated.

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