Alerting feature

The user should be able to set thresholds for alerting. For example:
- ~~If the soil moisture does not increase after irrigation~~
- If the irrigation flow rate does not increase after triggering automated irrigation
- If water flow exceeds a certain amount (how to detect leaks). Usage alerts (x gallons of water per y time period).
- If there is a large gap (i.e. outage) in data from sensors (or no heartbeat / status from solenoids)
- etc.

To accomplish this, the NodeFlow server should examine the incoming data, decide if any alert trigger has tripped, and then alert the user accordingly.

Building off of the ENTS-backend alerting API to implement higher order (conditional / chained) alerting.

The alert method should be selectable from:
- Email
- Text message
- Integration with messaging apps?