use codecov action

[brettmc]

our previous method of uploading to codecov.io is suffering from throttling and taking 5+ hours, a post in the opentelemetry maintainers channel suggests this is the way to do it now

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.31%. Comparing base (e44f5a9) to head (b0984f0).
Report is 6 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1294      +/-   ##
============================================
- Coverage     77.25%   74.31%   -2.95%     
- Complexity     2230     2391     +161     
============================================
  Files           321      349      +28     
  Lines          6682     7124     +442     
============================================
+ Hits           5162     5294     +132     
- Misses         1520     1830     +310     

Flag	Coverage Δ
8.1	74.31% <ø> (-2.95%)	⬇️
8.2	74.31% <ø> (-2.95%)	⬇️
8.3	74.31% <ø> (-2.95%)	⬇️
8.4	73.18% <ø> (-4.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 8 files with indirect coverage changes

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