Enable docker containers for TLS Interception

[abhinavsingh]

• Enable TLS interception from within docker containers. See https://github.com/abhinavsingh/proxy.py/tree/shared-argparse#tls-interception-with-docker
• Also, initial work aimed towards enabling shared arg parse. Plugins will be able to define their own custom flags.

[codecov]

Codecov Report

Merging #375 into develop will increase coverage by 0.01%.
The diff coverage is 91.17%.

@@             Coverage Diff             @@
##           develop     #375      +/-   ##
===========================================
+ Coverage    81.45%   81.47%   +0.01%     
===========================================
  Files           72       72              
  Lines         2810     2813       +3     
===========================================
+ Hits          2289     2292       +3     
  Misses         521      521              

Impacted Files	Coverage Δ
proxy/common/flags.py	97.80% <88.46%> (-0.06%)	⬇️
proxy/common/constants.py	100.00% <100.00%> (ø)

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[abhinavsingh]

@whitespots Haven't pushed docker image yet, but you can build one locally and give it a try. Refer to documentation here https://github.com/abhinavsingh/proxy.py/tree/shared-argparse#tls-interception-with-docker , need to polish a few things before merge and release.

Lemme know if you encounter any issues. Thank you!!!

[abhinavsingh]

@Benouare @httpnotonly @ja8zyjits @roshanprince402 @tawmoto folks jFYI