push built docs on release only

[amoodie]

separate out docs build to publish docs only on release of a new version. docs still built every PR and merge as part of regular testing.

This will help get in the habit of regular and frequent small releases (only way to update online docs is with a version release!)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.80%. Comparing base (16e776b) to head (cf24dd7).
⚠️ Report is 7 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #302      +/-   ##
===========================================
+ Coverage    78.49%   78.80%   +0.30%     
===========================================
  Files           12       12              
  Lines         2674     2675       +1     
===========================================
+ Hits          2099     2108       +9     
+ Misses         575      567       -8     

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