Add dashboard

Using google_monitoring_dashboard, create a dashboard for Cloud Run services akin to the manually created dashboard for Raven WebAuth.

The dashboard should contain:

• Request counts broken down by response code class (probably ignoring 404s).
• Request latencies for 50th, 95th and 99th percentile.
• Container CPU and memory utilitations for 50th, 95th and 99th percentile.
• Container instance count and billable instance time.