Use errgroup instead of counting goroutines

[cpuguy83]

What this PR does / why we need it:
Use errgroup instead of counting goroutines for syncing multiple goroutines.
This is much safer for future modification.

[jackfrancis]

/lgtm pending E2E thanks @cpuguy83!

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpuguy83, jackfrancis

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[codecov]

Codecov Report

Merging #3387 into master will decrease coverage by 0.06%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master    #3387      +/-   ##
==========================================
- Coverage   54.59%   54.52%   -0.07%     
==========================================
  Files         104      104              
  Lines       15778    15750      -28     
==========================================
- Hits         8614     8588      -26     
+ Misses       6412     6411       -1     
+ Partials      752      751       -1