review classifier: export request, verdict, check and run metrics, with a dashboard

The controller counts review requests, verdicts and per-check results and times each run; the classifier service counts retried asks. A provisioned Grafana dashboard charts them.

swarm-controller/src/review_classifier.rs

@@ -40,6 +40,7 @@ use self::settings::{Settings, SettingsSource};
 use crate::forge::{self, DefaultBranchFiles, PullForReview};
 use crate::routes::{AppState, error_problem};
 
+pub(crate) mod metrics;
 pub(crate) mod open_pr;
 pub(crate) mod review;
 pub(crate) mod runs;