Adding webhooks for when scheduled job starts running, and finishes

[mshamash]

It would be useful to have webhooks available for when a job just starts running, or when it finishes running (success or fail).
Now the webhooks for jobs/tools/workflows are limited to only when they're scheduled (https://docs.galaxyproject.org/en/release_20.01/admin/special_topics/webhooks.html)

Following up on this thread from the forums - https://help.galaxyproject.org/t/web-hook-post-to-external-url-when-job-begins-and-completes-running

[jmchilton]

I've long wanted post workflow actions, it would be much easier/performant to cleanup old data if we had a point where we knew for sure the workflow was done executing and scheduling for instance. That would be a good first step for doing this.