feat: don't ask for password when DB exists

[betodealmeida]

SUMMARY

When importing a dataset/chart/dashboard/saved query referencing databases that already exist, we shouldn't prompt for the password again.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before, every time we import something that depends on a database with a password we would prompt the user for it.

After, we no longer prompt for the password.

TESTING INSTRUCTIONS

1. Create a DB connection that has a password.
2. Create a dataset and then a chart; export chart.
3. Delete the chart and import it. It will import without prompting for the password.
4. Delete everything and import the chart. It will prompt for the password before importing.

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

[codecov]

Codecov Report

Merging #17776 (09bd6ca) into master (82b47ca) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #17776      +/-   ##
==========================================
+ Coverage   67.71%   67.78%   +0.06%     
==========================================
  Files        1605     1605              
  Lines       64198    64205       +7     
  Branches     6790     6790              
==========================================
+ Hits        43474    43522      +48     
+ Misses      18868    18827      -41     
  Partials     1856     1856              

Flag	Coverage Δ
hive	81.79% <100.00%> (-0.01%)	⬇️
mysql	82.17% <100.00%> (+<0.01%)	⬆️
postgres	82.22% <100.00%> (+<0.01%)	⬆️
presto	82.08% <100.00%> (?)
python	82.70% <100.00%> (+0.14%)	⬆️
sqlite	81.90% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
superset/charts/commands/importers/v1/__init__.py	100.00% <100.00%> (ø)
superset/databases/schemas.py	98.47% <100.00%> (+0.02%)	⬆️
superset/migrations/env.py	0.00% <0.00%> (ø)
superset/config.py	91.63% <0.00%> (+0.02%)	⬆️
superset/models/core.py	90.00% <0.00%> (+0.73%)	⬆️
superset/connectors/sqla/models.py	88.42% <0.00%> (+1.34%)	⬆️
superset/db_engine_specs/presto.py	89.97% <0.00%> (+5.63%)	⬆️

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[AAfghahi]

thank you for this!