[confighttp] Remove pointers from integer fields

[evan-bradley]

Description

I was looking through our defaults for a few confighttp.ClientConfig fields and found that 0 disables these fields in the underlying http.Transport object, which means we don't need them to be pointers.

Docs for the four fields we set in http.Transport here: https://pkg.go.dev/net/http#Transport.MaxIdleConns

I also stopped assigning defaults to any fields we take from http.DefaultTransport where setting them is a no-op since they aren't set in http.DefaultTransport.

Link to tracking issue

Helps unblock confighttp 1.0 from depending on #9478

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.37%. Comparing base (765e4a5) to head (e7ef178).
Report is 69 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12323      +/-   ##
==========================================
- Coverage   91.39%   91.37%   -0.03%     
==========================================
  Files         468      468              
  Lines       25591    25614      +23     
==========================================
+ Hits        23390    23405      +15     
- Misses       1785     1793       +8     
  Partials      416      416              

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[codeboten]

I'm ok with removing the pointers here, just one question