Drop attributes with a value of None

[hmstepanek]

Overview

This PR attempts to align the Python agent with the agent spec by dropping attributes with a value of None.

According to the spec:

Agents SHOULD NOT report null attribute values. The behavior of IS NULL queries in insights makes it so that omitted keys behave the same as null keys. Since there is no difference between omitting the key and sending a null, we SHOULD reduce the payload size by omitting null values from the payload entirely.

Since there should not be a difference in behavior for customers recording null attributes versus customers omitting an attribute, agents SHOULD add debug logging when a null value is recorded. This will give agents observability on recording of null attributes outside of audit logs.

"empty" values such as "" and 0 MUST be sent as an attribute in the payload.

It also performs some minor cleanup and adds descriptions to some function inside our attribute filtering system.
It also contains a fix for previously failing sklearn tests due to a non integer version: 0.0.post12.

Recommended review strategy: review each commit one at a time.

[github-actions]

🦙 MegaLinter status: ❌ ERROR

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	bandit	6		0	5.4s
✅ PYTHON	black	14	0	0	1.92s
✅ PYTHON	flake8	14		0	1.04s
✅ PYTHON	isort	14	0	0	0.33s
❌ PYTHON	pylint	14		30	7.53s

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6fd639d) 76.36% compared to head (03c1f50) 76.37%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1064   +/-   ##
=======================================
  Coverage   76.36%   76.37%           
=======================================
  Files         190      190           
  Lines       19747    19748    +1     
  Branches     3468     3470    +2     
=======================================
+ Hits        15080    15082    +2     
  Misses       3656     3656           
+ Partials     1011     1010    -1     

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[TimPansino]

Left comments, I've reviewed all the commits and it looks mostly good overall.