Return the RequestResponse instead of just awaiting and discarding

[seaders]

The response's data here contains data of the created Task which is vital for identifying purposes like deleting the task later, it makes no sense to just discard, and is different to what occurs with the cloud task library.

I opened a discussion about this: https://github.com/firebase/firebase-admin-node/issues/2791

But, after being extremely blocked by this issue, I remade the client for local tests, and confirmed that just returning the request gives everything needed.

Testing

All tests passed.