Alerting: support ok state in alert migration (#45264) (#45267)

(cherry picked from commit c59567a236)

Co-authored-by: Yuriy Tseretyan <yuriy.tseretyan@grafana.com>

pkg/services/sqlstore/migrations/ualert/alert_rule.go

@@ -262,6 +262,8 @@ func transExecErr(s string) (string, error) {
 		// Keep last state is translated to error as we now emit a
 		// DatasourceError alert when the state is error
 		return "Error", nil
+	case "ok":
+		return "OK", nil
 	}
 	return "", fmt.Errorf("unrecognized Execution Error setting %v", s)
 }