Mask proxy url credentials

[zhan9san]

Fix #2422

Could you kindly review this PR?

[jonchapmansai]

How do we get this reviewed?

[nateprewitt]

Hi @zhan9san, thanks for the PR! We've added some minor changes and tests. We're working on doing final validation and will look to get this merged in an upcoming release.

[codecov-commenter]

Codecov Report

Merging #2543 (eaa4061) into develop (26528a5) will increase coverage by 0.11%.
The diff coverage is 71.42%.

@@             Coverage Diff             @@
##           develop    #2543      +/-   ##
===========================================
+ Coverage    95.32%   95.43%   +0.11%     
===========================================
  Files           59       59              
  Lines        11474    11842     +368     
===========================================
+ Hits         10938    11302     +364     
- Misses         536      540       +4     

Impacted Files	Coverage Δ
botocore/httpsession.py	91.35% <71.42%> (-0.54%)	⬇️
botocore/signers.py	98.17% <0.00%> (-0.46%)	⬇️
botocore/utils.py	95.64% <0.00%> (-0.07%)	⬇️
botocore/args.py	100.00% <0.00%> (ø)
botocore/config.py	100.00% <0.00%> (ø)
botocore/serialize.py	100.00% <0.00%> (ø)
botocore/docs/client.py	100.00% <0.00%> (ø)
botocore/parsers.py	99.45% <0.00%> (+<0.01%)	⬆️
botocore/credentials.py	98.66% <0.00%> (+0.01%)	⬆️
... and 9 more

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[jonchapmansai]

Thank you @zhan9san @nateprewitt @joguSD
I really appreciate your work improving that