Support pausing & resuming autostop

[concretevitamin]

From @dongreenberg: he'd like to have an API to temporarily pause autostop, due to some activity happening (e.g., running Jupyter) that is not captured in our job queue. After the activity finishes, he'd like the autostop setting to resume.

There's some workaround at the moment, but if this is officially supported he'd like to switch to these APIs.