observability: convert frontend dashboard to generated
Created by: slimsag
This is a nearly direct translation of the current frontend dashboard and rules to the new generator.
Before:
After:
Notable mentions here:
- Those line removal / addition counts are no joke :)
- It's far easier to see when our warning/critical thresholds have been wrong for Sourcegraph.com in the past -- quite nice!
- "hard error" no longer appears twice, and it's now clear that there were none in the past 7 days
- "Internal service requests" is now collapsed by default, under the premise that nobody should be looking at these unless an alert about them is firing.
Fixes #9356 (closed) Fixes #9660 (closed)