Provide a way to configure a list of banned workers

[dukejansen]

I occasionally encounter a worker that consistently generates a static/useless image. It would be nice to be able to prevent my jobs from going to that worker.

[dukejansen]

I guess I see this as somewhat analogous to, or perhaps an extension of, the dropdown that lets me choose a specific worker to send all my work to. Ideally both would be a multi-select, so I could choose to only send work to Workers W and X, or I could choose to never send work to Workers Y and Z. 🤔