Add sendAlert method on mesh interface

[thebentern]

I don't want this on the CLI, but I do want it on the API for the lib for integrators

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 61.03%. Comparing base (4e267c7) to head (d161291).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
meshtastic/mesh_interface.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #724      +/-   ##
==========================================
+ Coverage   61.01%   61.03%   +0.01%     
==========================================
  Files          24       24              
  Lines        3907     3911       +4     
==========================================
+ Hits         2384     2387       +3     
- Misses       1523     1524       +1     

Flag	Coverage Δ
unittests	61.03% <75.00%> (+0.01%)	⬆️

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