bluetooth/gst: Timestamp encoding buffers according to PA clock

Commit c6d6ca54 ("bluetooth/gst: Replace buffer accumulation in adapter
with direct pull") removed the `timestamp` parameter from GStreamer
transcoders due to being unused, but these should instead be propagated
to the GStreamer encoding buffers.
2 jobs for gst-synchronous in 4 minutes and 17 seconds (queued for 1 second)
Status Name Job ID Coverage
  Container
passed build-container #15177401

00:00:22

 
  Build
passed build-meson #15177402

00:03:54