Improve documentation

[villebro]

CATEGORY

Choose one

• Bug Fix
• Enhancement (new features, refinement)
• Build / Development Environment
• Documentation

SUMMARY

I was working on something unrelated and noticed the need to change the following:

• Some documentation was emitting errors (incorrect headers etc)
• No documentation for current_user_id and current_username jinja functions
• Bump Sphinx deps and add support for type annotations (added dependency on MIT licensed sphinx_autodoc_typehints)

TEST PLAN

Tested locally

BEFORE

AFTER

REVIEWERS

@mistercrunch @john-bodley

[codecov-io]

Codecov Report

Merging #7813 into master will decrease coverage by <.01%.
The diff coverage is 64.28%.

@@            Coverage Diff             @@
##           master    #7813      +/-   ##
==========================================
- Coverage   65.89%   65.89%   -0.01%     
==========================================
  Files         459      459              
  Lines       22011    22016       +5     
  Branches     2417     2417              
==========================================
+ Hits        14505    14507       +2     
- Misses       7385     7388       +3     
  Partials      121      121

Impacted Files	Coverage Δ
superset/jinja_context.py	75.26% <64.28%> (-2.01%)	⬇️

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[john-bodley]

This is sweet.

[villebro]

I'll go ahead and merge this right away, I have another PR that is partially dependent on this.