features: making client tracing opt-in

[mattklein123]

Due to tokio-rs/tracing#3521 I would like to request that this feature be opt-in.

[mattklein123]

Let me know if you want it to default on and I can figure that out but I would like some way of turning off tracing on hyper-util. Thank you.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.5%. Comparing base (796b90d) to head (e883f2a).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1972     +/-   ##
=======================================
+ Coverage   76.5%   76.5%   +0.1%     
=======================================
  Files         89      89             
  Lines       8587    8590      +3     
=======================================
+ Hits        6563    6568      +5     
+ Misses      2024    2022      -2     

see 8 files with indirect coverage changes

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[clux]

Hey, thanks for raising this. From upstream comments it makes sense to have it as opt-in until direction/consensus is more clear.

Obviously not super happy about having an extra feature for a workaround, but I guess it could be removed in the future if there's a better solution upstream. Waiting a week to see if there are other opinions, otherwise will probably ship this in 4.0.