Re-add support for basic auth in Proxy

[goenning]

Motivation

When kube-rs moved from hyper-http-proxy to hyper-util, support for Basic Auth was lost as this was previously done inside the crate.

Solution

This PR adds support for auth again inside kube-rs as it seems like the hyper-util is avoiding anything new being added to their legacy modules.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.3%. Comparing base (ab9040e) to head (3868808).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
kube-client/src/client/builder.rs	0.0%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1959     +/-   ##
=======================================
+ Coverage   76.3%   76.3%   +0.1%     
=======================================
  Files         89      89             
  Lines       8507    8512      +5     
=======================================
+ Hits        6486    6492      +6     
+ Misses      2021    2020      -1     

Files with missing lines	Coverage Δ
kube-client/src/client/builder.rs	69.7% <0.0%> (-2.7%)	⬇️

... and 4 files with indirect coverage changes

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[clux]

this seems sensible to me. thank you.