Support for device-attribute "Alert" missing

[JunkerMartin]

"alert" is described in the "AVM Home Automation HTTP Interface" - Doc 1.36 from 2020/09/16 and is shown for me with the device "blind".

Sample:
```
<alert>
<state>0</state>
<lastalertchgtimestamp>1637521201</lastalertchgtimestamp>
</alert>

[TDesjardins]

@JunkerMartin Seems this is also already solved with your patch:

fritzbox-java-api/src/main/java/com/github/kaklakariada/fritzbox/model/homeautomation/Device.java

Line 79 in e06cb65

private Alert alert;