feat: postgres connection form

[eschutho]

SUMMARY

This PR adds the functionality of calling databases/available api to get a list of databases that have drivers loaded and available to use. The form is built dynamically based on that information. This is currently behind a local flag, and there are no visual changes, but the piece in development is as shown below. More work is needed to hook the form up to the api on connect/save, but I'm merging often to reduce any rebasing issues and also keep PRs small.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

This is behind a local flag useSqlAlchemyForm which is set to 'false'

TEST PLAN

visual changes only right now, so all existing tests should pass

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

[eschutho]

this is hardcoded for now, and doesn't do anything unless useSqlAlchemyForm is true. Eventually the db will be chosen by the user on a different step.

[codecov]

Codecov Report

Merging #14456 (6e508bd) into master (6d786d4) will decrease coverage by 0.03%.
The diff coverage is 44.77%.

@@            Coverage Diff             @@
##           master   #14456      +/-   ##
==========================================
- Coverage   77.40%   77.37%   -0.04%     
==========================================
  Files         958      959       +1     
  Lines       48329    48388      +59     
  Branches     5679     5689      +10     
==========================================
+ Hits        37410    37438      +28     
- Misses      10719    10750      +31     
  Partials      200      200              

Flag	Coverage Δ
javascript	72.40% <44.77%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...RUD/data/database/DatabaseModal/SqlAlchemyForm.tsx	100.00% <ø> (ø)
...c/views/CRUD/data/database/DatabaseModal/styles.ts	69.86% <13.04%> (-26.14%)	⬇️
...tend/src/views/CRUD/data/database/DatabaseList.tsx	80.37% <25.00%> (-0.76%)	⬇️
...c/views/CRUD/data/database/DatabaseModal/index.tsx	56.77% <57.14%> (+0.17%)	⬆️
.../database/DatabaseModal/DatabaseConnectionForm.tsx	64.28% <64.28%> (ø)
superset-frontend/src/views/CRUD/hooks.ts	46.97% <100.00%> (+1.78%)	⬆️
superset-frontend/src/views/store.ts	100.00% <0.00%> (ø)
superset-frontend/src/dashboard/actions/hydrate.js	1.75% <0.00%> (ø)

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[eschutho]

This pr is dependent on #14470

[eschutho]

Rerunning tests.

[eschutho]

the functionality is set up in the next PR that has the save db: #14583

[eschutho]

A significant enough portion of this PR has changed now that would warrant me closing it and leaving just the save PR for review.