Implement can_write_network_settings API

[puddly]

See zigpy/zigpy#1616

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.51%. Comparing base (9bb0cf7) to head (064b922).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #687      +/-   ##
==========================================
+ Coverage   99.46%   99.51%   +0.05%     
==========================================
  Files          58       58              
  Lines        3915     3924       +9     
==========================================
+ Hits         3894     3905      +11     
+ Misses         21       19       -2     

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