executor: Add metrics dashboard

Created by: efritz

The executor currently emits no useful metrics and has no dashboard of its own. We should be emitting metrics for

• number of firecracker vms running
• number of firecracker commands failings
• job failure rate
• job latency

We also need to figure out a way to get things like memory and CPU usage from the other GCP project. The difficulty of this task is unknown and we may de-scope if we find it's not achievable within the estimate for this issue.