Uploads a custom sermon thumbnail to SermonAudio (encoding options → media slot → binary POST).
Failures return { ok: false } so callers can log without aborting the main upload job.
Parameters
input: UploadSermonAudioThumbnailInput
Sermon id, API key, thumbnail stream, content type, and optional abort signal.
Uploads a custom sermon thumbnail to SermonAudio (encoding options → media slot → binary POST). Failures return
{ ok: false }so callers can log without aborting the main upload job.