feat(auth): add proxy-server authentication

[EndlessParadox1]

Function BasicAuth is not suitable for proxy-server authentication, so I add a brand new function BasicAuthForProxy in auth.go and test it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.36%. Comparing base (3dc1cd6) to head (bd0dd5d).
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3877      +/-   ##
==========================================
+ Coverage   99.21%   99.36%   +0.15%     
==========================================
  Files          42       43       +1     
  Lines        3182     2689     -493     
==========================================
- Hits         3157     2672     -485     
+ Misses         17        9       -8     
  Partials        8        8              

Flag	Coverage Δ
	?
-race	∅ <ø> (?)
-tags "sonic avx"	99.36% <100.00%> (?)
-tags go_json	99.36% <100.00%> (?)
-tags nomsgpack	99.35% <100.00%> (?)
go-1.18	99.29% <100.00%> (+0.17%)	⬆️
go-1.19	99.36% <100.00%> (+0.15%)	⬆️
go-1.20	99.36% <100.00%> (+0.15%)	⬆️
go-1.21	99.36% <100.00%> (+0.15%)	⬆️
go-1.22	99.36% <100.00%> (?)
macos-latest	99.36% <100.00%> (+0.15%)	⬆️
ubuntu-latest	99.36% <100.00%> (+0.15%)	⬆️

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