review-classifier: skip draft prs, classify once when they leave draft

swarm-controller/src/review_classifier/metrics.rs

@@ -32,6 +32,8 @@ pub(super) enum Request {
     Started,
     /// Taken for a head already reviewed; its verdict was posted again.
     Reposted,
+    /// Taken for a PR the forge calls a draft; nothing ran or posted.
+    Draft,
 }
 
 impl Request {
@@ -43,6 +45,7 @@ impl Request {
             Self::Deferred => "deferred",
             Self::Started => "started",
             Self::Reposted => "reposted",
+            Self::Draft => "draft",
         }
     }
 }