* add the last_heartbeat field
* add heartbeat controller
* add endpoint of heartbeat
* heartbeat integration
* add last_heartbeat to cscli machines list
- Don't allow running more than one alert flush job at a time to prevent runaway CPU usage in some case. (fix High CPU after Upgrade to 1.2.0 #1022)
- Add a cscli alerts flush command to manually flush the alerts in the database (fixes Improvement/Manual flush mechanism #1023 ).
- Enable cascading deletion on alerts as we upgraded ent: Deleting an alert in the database will automatically delete all related decisions, events and meta
- Add an index on alerts.id to try to improve flush performance with very big sqlite database.
- Flush alert now operates in batch