move pkg/health out of registry-scanner

[ishitasequeira]

Based on discussion in #972 (comment), moving the package pkg/health out of registry-scanner.

Also, add step for publishing code coverage of registry-scanner to codecov.io

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.07%. Comparing base (d07cf71) to head (371a96f).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #995      +/-   ##
==========================================
+ Coverage   71.99%   72.07%   +0.08%     
==========================================
  Files          24       25       +1     
  Lines        3642     3653      +11     
==========================================
+ Hits         2622     2633      +11     
  Misses        880      880              
  Partials      140      140              

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