Delay before sending a high/low temperature alert

[jmbrunskill]

Is your feature request related to a problem? Please describe

When a Fridge or freezer is running close to its temperature limit, small fluctuations could cause a lots of alarms.

Describe the solution you'd like

The system should wait a configured period of time before sending the alert (should probably be 2-3 expected samples so often 15 minutes in practice)

Acceptance Criteria

• Alerts are only triggered if the temperature is too high or too low for a configured period of time
• Ok message should be sent after the same period of time of being ok?

Describe alternatives you've considered

Set a higher limit so that we only get alerted when it's had time to get a higher temperature

Additional context