feat: webhook self call for Eventarc-triggered events

[nicain]

Solve retry issue by letting the webhook call itself, and escape any timeout errors so that the original call can still respond to pub/sub (the transport mechanism for the Eventarc call) with a 200 (i.e. request ack and send for processing).

[telpirion]

nit: get rid of the nested if. Since each branch of the condition returns a value, you can just use the guard pattern:

   if data.get("kind", None) == "storage#object":
        # Entrypoint called by Pub-Sub (Eventarc)
       return redirect_and_reply(data)

   if "bucket" in data:
       return cloud_event_entrypoint(
                name=data["name"],
                event_id=data["id"],
                bucket=data["bucket"],
                time_created=coerce_datetime_zulu(data["timeCreated"]),
            )
   if "text" in data:
       return summarization_entrypoint(
                name=data["name"],
                extracted_text=data["text"],
                time_created=datetime.datetime.now(datetime.timezone.utc),
                event_id="CURL_TRIGGER",
            )

[nicain]

Yes, this is much cleaner.