Add support for topic in Zulip notifications and truncate long topics

Subjects over 60 characters long, such as the test notification, are rejected by shoutrrr. This truncates the subject to the max length.

Users may want all Scrutiny notifications to be sent to a particular topic rather than whatever Scrutiny happens to decide.

webapp/backend/pkg/notify/notify.go

@@ -424,6 +424,17 @@ func (n *Notify) GenShoutrrrNotificationParams(shoutrrrUrl string) (string, *sho
 	case "telegram":
 		(*params)["title"] = subject
 	case "zulip":
+		query := serviceURL.Query()
+		urlTopic := query["topic"]
+		delete(query, "topic")
+		if len(urlTopic) > 0 && urlTopic[len(urlTopic)-1] != "" {
+			subject = urlTopic[len(urlTopic)-1]
+		}
+		subjectRunes := []rune(subject)
+		if len(subjectRunes) > 60 {
+			n.Logger.Warningf("Zulip notification subject too long (%d characters), truncating to 60 characters", len(subjectRunes))
+			subject = string(subjectRunes[:60])
+		}
 		(*params)["topic"] = subject
 	}