fix: DB parameter validation API

[betodealmeida]

SUMMARY

I was testing the new validation API for DB parameters and realized that it would fail in certain cases because the SIP-41 handler uses dataclasses.asdict, which doesn't play nice with defaultdict (https://bugs.python.org/issue35540).

I added custom code to handle the payload with defaultdict in case there's a validation error, converting to a normal dict.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TEST PLAN

Added a unit test covering the regression.

ADDITIONAL INFORMATION

• Has associated issue:
• 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

[codecov]

Codecov Report

Merging #14636 (d7c8a3a) into master (e4d2424) will decrease coverage by 0.00%.
The diff coverage is 75.00%.

❗ Current head d7c8a3a differs from pull request most recent head c9a7932. Consider uploading reports for the commit c9a7932 to get more accurate results

@@            Coverage Diff             @@
##           master   #14636      +/-   ##
==========================================
- Coverage   77.47%   77.47%   -0.01%     
==========================================
  Files         958      958              
  Lines       48486    48490       +4     
  Branches     5679     5679              
==========================================
+ Hits        37565    37568       +3     
- Misses      10721    10722       +1     
  Partials      200      200              

Flag	Coverage Δ
hive	80.96% <75.00%> (-0.01%)	⬇️
mysql	81.24% <75.00%> (-0.01%)	⬇️
postgres	81.26% <75.00%> (-0.01%)	⬇️
presto	80.96% <75.00%> (-0.01%)	⬇️
python	81.79% <75.00%> (-0.01%)	⬇️
sqlite	80.88% <75.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
superset/databases/schemas.py	99.54% <ø> (ø)
superset/databases/api.py	92.17% <75.00%> (-0.25%)	⬇️

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