Consider using Qiskit Serverless for cron job notebook testing

[Eric-Arellano]

In our cron job, we run every notebook that submits jobs:

documentation/.github/workflows/notebook-test-cron.yml

Line 33 in 83573cc

run: tox -- --write --only-submit-jobs

But the jobs might take longer than GH Actions' 6 hour limit when there is a long queue. Notably, we cannot batch the different jobs because they are distinct notebooks so using with Batch is not viable. We now use concurrency with asyncio, but we still can exceed the time limit.

So, instead, @frankharkins had the great idea of using Qiskit Serverless. On day 1, we'd submit all the notebooks to Qiskit Serverless. On day 2, a new cron job would run that retrieves the results from Qiskit Serverless.

Question: what workflow do we want for local runs?

[frankharkins]

Putting this on hold for a bit as the action is actually doing OK at the moment and we might be able to get higher priority if it starts being a problem again. I'm worried serverless would add yet another layer of things to go wrong.