Read the network key if the firmware supports it

[puddly]

v3.A0 added a command to read the network key (back in February 😅). This allows a ZiGateV2 running the latest firmware to create a functional network backup that can be restored on a better-supported radio.

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (697b649) 46.94% compared to head (b057c68) 47.08%.

Files	Patch %	Lines
zigpy_zigate/api.py	60.00%	4 Missing :warning:
zigpy_zigate/zigbee/application.py	66.66%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #152      +/-   ##
==========================================
+ Coverage   46.94%   47.08%   +0.14%     
==========================================
  Files           9        9              
  Lines        1357     1372      +15     
==========================================
+ Hits          637      646       +9     
- Misses        720      726       +6     

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