Add Transcript deletion support

[ploeber]

Support https://www.assemblyai.com/docs/api-reference/transcript#delete-a-transcript
-> Add Transcript.delete_by_id() and delete_by_id_async()

[Swimburger]

Based on what I've seen from the Python SDK, you can call methods on the transcript.
Maybe delete could be added as an instance method too, like my_transcript.delete() and my_transcript.delete_async().