PR-56: Add direct data execution

[PRodriguezFlores]

• Added feature where the models can be executed directly with druid data, not only with druid queries.
• Provided test for new functionality.
• Refactored API logic.
• Added example script of how to use the service.
• Updated README to include the example.
• Simplified loss function used by the model and updated the model to be compatible with said loss function.
• Updated the project to python 3.9.
• Updated requirements.txt.

[the-label-bot]

The Label Bot has predicted the following:

Category	Value	Confidence	Applied Label
Kind	feature	0.829	✔️
Kind	XL	0.832	✔️

[codecov]

Codecov Report

Attention: Patch coverage is 95.74468% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 83.17%. Comparing base (517564a) to head (72806ad).
Report is 2 commits behind head on master.

Files	Patch %	Lines
resources/src/server/rest.py	95.65%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #60      +/-   ##
==========================================
+ Coverage   82.95%   83.17%   +0.22%     
==========================================
  Files          13       13              
  Lines         745      755      +10     
==========================================
+ Hits          618      628      +10     
  Misses        127      127              

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[malvads]

lgtm