Added specs-url-scheme option for Api.

[DustinMoriarty]

• Support explicitly setting the scheme for specs_url for the swagger.json file for cases where the URL scheme does not resolve correctly such as when deploying on AWS ECS behind an elastic load balancer. Behavior is unchanged for cases where the keyword argument is left as None. See Need to Explicitly set Swagger specs_url Scheme When Deployed on Behind AWS Elastic Load Balancer. #237
• Added tests for the new behavior as well as to confirm the old behavior has not changed.
• Added docstrings.
• Formatted with black. This will effect the diff for a few other modules such as flask_restx/reqparse.py, flask_restx/model.py. flask_restx/inputs.py and some other locations in api.py.
• Added .python-version and .idea to .gitignore.

[codecov]

Codecov Report

Merging #238 (0e8cd95) into master (b0ea3be) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #238   +/-   ##
=======================================
  Coverage   96.87%   96.88%           
=======================================
  Files          20       20           
  Lines        2724     2727    +3     
=======================================
+ Hits         2639     2642    +3     
  Misses         85       85           

Impacted Files	Coverage Δ
flask_restx/api.py	96.71% <100.00%> (+0.02%)	⬆️

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[DustinMoriarty]

@mas15 OR @j5awry : Can this be merged? Thank you.

[mas15]

@DustinMoriarty Hi, I cannot do that since I am not a maintainer. This project is abandoned and I would not expect this to be merged

[DustinMoriarty]

To bad. Thanks for letting me know.

[DustinMoriarty]

@j5awry : I updated this to get it up to date with the upstream. I do need maintainer approval to get it through the workflow checks and merge if you think this is something you would like to do.

[j5awry]

Thanks for your contribution, and for taking the time to update this after we moved ahead! LGTM