chore: Extensions architecture POC

[michael-s-molina]

SUMMARY

This branch is for POC purposes and should not be merged to master.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

To access the POC, use the SQL -> SQL Lab POC menu option.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[korbit-ai]

Based on your review schedule, I'll hold off on reviewing this PR until it's marked as ready for review. If you'd like me to take a look now, comment /korbit-review.

Your admin can change your review schedule in the Korbit Console

[codecov]

Codecov Report

Attention: Patch coverage is 70.00000% with 18 lines in your changes missing coverage. Please review.

Project coverage is 65.52%. Comparing base (76d897e) to head (5b83a71).
Report is 1463 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/extensions/api.py	54.05%	17 Missing ⚠️
superset/views/sqllab_poc.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #31934      +/-   ##
==========================================
+ Coverage   60.48%   65.52%   +5.04%     
==========================================
  Files        1931      548    -1383     
  Lines       76236    39157   -37079     
  Branches     8568        0    -8568     
==========================================
- Hits        46114    25659   -20455     
+ Misses      28017    13498   -14519     
+ Partials     2105        0    -2105     

Flag	Coverage Δ
hive	48.53% <70.00%> (-0.64%)	⬇️
javascript	?
presto	53.05% <70.00%> (-0.75%)	⬇️
python	65.52% <70.00%> (+2.04%)	⬆️
unit	61.08% <70.00%> (+3.45%)	⬆️

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[michael-s-molina]

@villebro @rusackas Here are the 2 extensions that I wrote as examples: extensions.zip