Implement action feature

[rytilahti]

Adds FeatureType.Action making it possible to expose features like "reboot", "test alarm", "pair" etc.

The attribute_getter is no longer mandatory, but it will raise an exception if not defined for other types than actions.
Trying to read returns a static string <Action>.
This overloads the set_value to call the given callable on any value.

This also fixes the play and stop coroutines of the alarm module to await the call.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (master@203bd79). Click here to learn what that means.
Report is 11 commits behind head on master.

Files	Patch %	Lines
kasa/smart/modules/alarmmodule.py	50.00%	2 Missing ⚠️
kasa/feature.py	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #849   +/-   ##
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  Coverage          ?   89.12%           
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  Files             ?       67           
  Lines             ?     4671           
  Branches          ?     1149           
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  Hits              ?     4163           
  Misses            ?      421           
  Partials          ?       87           

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[rytilahti]

Action might be a better name for this, considering how homeassistant-centric Button is.

[sdb9696]

lgtm