Added a check for existing healthz route to avoid overwriting user cu…

[antontroshin]

Description

Added a check for existing healthz route to avoid overwriting user custom handler

Issue reference

#579

Please reference the issue this PR will close: #579

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.17%. Comparing base (27248ba) to head (a2b727c).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #580      +/-   ##
==========================================
+ Coverage   58.04%   58.17%   +0.12%     
==========================================
  Files          55       55              
  Lines        3568     3574       +6     
==========================================
+ Hits         2071     2079       +8     
+ Misses       1375     1374       -1     
+ Partials      122      121       -1     

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[mikeee]

lgtm