speechmatics: expose unsynced pads on transcriber

commit d7f4351eef02ccf25851e229844d5bf2dd2121f7 (HEAD -> speechmatic-unsynced, moi/speechmatic-unsynced)
Author: Mathieu Duponchelle <mathieu@centricular.com>
Date:   Mon Dec 2 17:16:11 2024 +0100

    transcriberbin: register pad templates for unsynced source pads

commit a7ac980a2ebd227ef6fa23b0be4430f0995859b9
Author: Mathieu Duponchelle <mathieu@centricular.com>
Date:   Mon Dec 2 17:01:50 2024 +0100

    speechmatics: expose unsynced pads on transcriber
    
    This can be used for storing original transcripts for editing after the
    fact.
    
    Modeled on the aws transcriber, to be usable from transcriberbin.