aws_transcriber: expose lateness property
aws_transcriber: expose lateness property

The default behavior for the transcriber is to output text buffers
synchronized with the input stream, introducing a configurable
latency.

For use cases where synchronization is not crucial, but latency
is, the lateness property can be used instead of or in combination
with the latency property, in order to introduce a configurable
offset with the input stream.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/534>

sdroege/rsplugin,sdroege/rsplugin