feat: Expand grafana dashboard, bump to schemaVersion 38

- Bump dashboard to schemaVersion 38, from Grafana vesion 10.2.0.
- Add a "General overview" row.
- Filter the preexisting visualizations with
  `request_origin="validate"`.
- Add new visualizations pertaining audit requests, filtering with
  `request_origin="audit"`.
- Leave latency untouched.

Signed-off-by: Víctor Cuadrado Juan <vcuadradojuan@suse.de>

Author: viccuad