feat: fallback to external password store for sqlalchemy connections

[fbalicchia]

SUMMARY

Superset can be configured to use an external store for database passwords. This is useful if you a running a custom secret distribution framework and do not wish to store secrets in Superset’s meta database. This useful capability can be extended by providing Superset’s meta database as a fallback in the case the administration doesn't want to use an external store for a particular database

TESTING INSTRUCTIONS

Set SQLALCHEMY_CUSTOM_PASSWORD_STORE to point to an external lookup function. and the user does not have to check where her password is saved. Current tests must continue to work

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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a7a4561) 66.91% compared to head (b55c740) 72.21%. Report is 1910 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #20898      +/-   ##
==========================================
+ Coverage   66.91%   72.21%   +5.29%     
==========================================
  Files        1851     2025     +174     
  Lines       70709    92111   +21402     
  Branches     7766     7766              
==========================================
+ Hits        47316    66515   +19199     
- Misses      21371    23574    +2203     
  Partials     2022     2022              

Flag	Coverage Δ
hive	54.35% <84.61%> (+1.88%)	:arrow_up:
mysql	80.79% <100.00%> (+2.83%)	:arrow_up:
postgres	80.87% <100.00%> (+2.84%)	:arrow_up:
presto	54.33% <84.61%> (+1.97%)	:arrow_up:
python	84.55% <100.00%> (+3.27%)	:arrow_up:
sqlite	77.68% <90.90%> (+1.18%)	:arrow_up:
unit	55.14% <84.61%> (+3.95%)	:arrow_up:

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[fbalicchia]

Hi @hughhhh I'm sorry if I link directly but I saw that you have some commit on this piece of code. Could you please review this pr and if it has make sense to you

Thanks

[rusackas]

Sorry this slid under everyone's radar for so long. Adding @dpgaspar for a security perspective, and closing/reopening to reboot the CI process.