Provide shell completion for cz

[danvergara]

Description

As mentioned in #137 , this PR add auto-completion to cz using argcomplete

Checklist

• Add test cases to all the changes you introduce
• Run ./script/format and ./script/test locally to ensure this change passes linter check and test
• Test the changes on the local machine manually
• Update the documentation for the changes

Expected behavior

If the proper activation is set, the auto-completion can performed just by pressing the
tab key.

Steps to Test This Pull Request

1. Run the tests
2. Activate the virtual environment provided by the project/Poetry
3. Activate the auto-completion. For one-time activation of argcomplete for Commitizen only, use:
   $ eval "$(register-python-argcomplete cz)"
4. Type incomplete commands and flags from Commitizen and just pres the tab key.

Additional context

Related to #137

[codecov]

Codecov Report

Merging #305 (61c13e4) into master (720befe) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #305   +/-   ##
=======================================
  Coverage   96.96%   96.97%           
=======================================
  Files          33       33           
  Lines         924      926    +2     
=======================================
+ Hits          896      898    +2     
  Misses         28       28           

Flag	Coverage Δ
unittests	96.97% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
commitizen/__version__.py	100.00% <100.00%> (ø)
commitizen/cli.py	97.50% <100.00%> (+0.13%)	⬆️

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[Lee-W]

This one looks good to me. I also tested it locally and it works. @woile Could you please check this one? Thanks 🙂

[woile]

Thanks a lot!