Fix missing DB patch and use DATETIME as column format

db/patch-heartbeat-add-last-notified-time.sql

@@ -0,0 +1,7 @@
+-- You should not modify if this have pushed to Github, unless it does serious wrong with the db.
+BEGIN TRANSACTION;
+
+ALTER TABLE heartbeat
+    ADD last_notified_time DATETIME default null;
+
+COMMIT;