rtspsrc: proxy new "add-reference-timestamp-meta" property from rtpjitterbuffer

When syncing to an RFC7273 clock this will add the original
reconstructed reference clock timestamp to buffers in form
of a GstReferenceTimestampMeta.

This is useful when we want to process or analyse data based
on the original timestamps untainted by any local adjustments,
for example reconstruct AES67 audio streams with sample accuracy.

Part-of: <gstreamer/gstreamer!1964>
24 jobs for !1964 with rtpjitterbuffer-rfc7273-ref-timestamp-meta in 43 minutes and 19 seconds (queued for 2 seconds)
merge request