Default task for result inserts as null

[WrathfulSpatula]

(See unitaryfund/metriq-app#149.)

I've run into a case where, if I try to add a new result to the "VQE" submission, with the default "VQE" task, then the task is actually inserted as null, for the result document. The POST API should reject the result insertion, if it lacks either a task or a method.

@vprusso If you want to take this issue, on the API call validation side, please do. I can update the front end side, correspondingly. This isn't a blocker for me, so long as I at least update the front end, now.

[vprusso]

Cool, let me take a stab at handling this on the API side. Thanks!

[vprusso]

Closing this issue as it appears to be a pure frontend issue as per our discussion.