Add monitoring

[Overtorment]

Workers should have a heartbeat, and some kind of reporting if there's no heartbeat. Also, MySQL queries used to get stuck indefinitely till worker restarted, so some kind of monitoring for blockchain tip would be nice. It hasn't happened for a while since Ive made some fixes, but anyway...

MariaDB [n5fno50p7elj9fbn]> select * from key_value ;
+----------------------+--------+
| key                  | value  |
+----------------------+--------+
| LAST_PROCESSED_BLOCK | 643083 |
+----------------------+--------+
1 row in set (0.08 sec)