Arvados

Specific test case: running a workflow with 100s of containers and then canceling them all at once leads to a massive surge of requests to the API server as all the containers finalize all at once.

Want to test ways that we can mitigate this traffic surge so that:

1. all the containers finalize without fatal 503 errors (#20540, #20541)
2. the workbench remains responsive (at least for GET requests during this time)
   1. evaluate configuration changes
   2. load balancing #20539
   3. controller request prioritization #20602
   4. Send out cancellations at a slower rate than whatever it's doing right now