feat: Removed undici feature flag. This will now instrument undici by default

[bizob2828]

Description

I was hoping to remove the undici_async_tracking feature flag but there is still some inconsistency with async context propagation. This will need to be addressed in undici itself. I think I plan on PRing that shortly so that we can remove this feature flag at a later date.

Links

Closes #1771

[codecov]

Codecov Report

Merging #1772 (f30c62a) into main (3f494f8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1772   +/-   ##
=======================================
  Coverage   96.83%   96.83%           
=======================================
  Files         198      198           
  Lines       38747    38734   -13     
=======================================
- Hits        37520    37510   -10     
+ Misses       1227     1224    -3     

Flag	Coverage Δ
integration-tests-16.x	79.04% <100.00%> (ø)
integration-tests-18.x	79.05% <100.00%> (+<0.01%)	⬆️
integration-tests-20.x	79.06% <100.00%> (ø)
unit-tests-16.x	91.39% <100.00%> (+<0.01%)	⬆️
unit-tests-18.x	91.37% <100.00%> (+<0.01%)	⬆️
unit-tests-20.x	91.37% <100.00%> (+<0.01%)	⬆️
versioned-tests-16.x	75.56% <100.00%> (-0.04%)	⬇️
versioned-tests-18.x	75.56% <100.00%> (-0.04%)	⬇️
versioned-tests-20.x	75.57% <100.00%> (-0.03%)	⬇️

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Files Changed	Coverage Δ
lib/feature_flags.js	100.00% <100.00%> (ø)
lib/instrumentation/undici.js	99.11% <100.00%> (+1.20%)	⬆️

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