fix(healthcheck): clone default transport to avoid nil pointer deref

[JosephKav]

and added tests for the health check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.82%. Comparing base (6f60f3a) to head (3e615a5).
⚠️ Report is 12 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #707   +/-   ##
=======================================
  Coverage   98.82%   98.82%           
=======================================
  Files         132      132           
  Lines        8891     8891           
=======================================
  Hits         8786     8786           
  Misses         80       80           
  Partials       25       25           

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