fix: make a new entrypoint for deprecated postgres dialect

[eschutho]

SUMMARY

Sqlalchemy 1.4 deprecated the postgres dialect and any existing Sqlalchemy URI strings that use postgres as opposed to the current postgresql will not work. This PR creates a new entry point that will map the old postgres dialect to the current postgresql one.

TESTING INSTRUCTIONS

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 #20895 (05ca57b) into master (383313b) will increase coverage by 0.01%.
The diff coverage is 66.66%.

❗ Current head 05ca57b differs from pull request most recent head 78d3e7c. Consider uploading reports for the commit 78d3e7c to get more accurate results

@@            Coverage Diff             @@
##           master   #20895      +/-   ##
==========================================
+ Coverage   66.27%   66.28%   +0.01%     
==========================================
  Files        1758     1758              
  Lines       67072    67039      -33     
  Branches     7122     7116       -6     
==========================================
- Hits        44453    44440      -13     
+ Misses      20800    20769      -31     
- Partials     1819     1830      +11     

Flag	Coverage Δ
hive	53.25% <56.52%> (+<0.01%)	⬆️
mysql	?
postgres	81.06% <78.26%> (-0.02%)	⬇️
presto	53.15% <56.52%> (+<0.01%)	⬆️
python	81.50% <78.26%> (-0.06%)	⬇️
sqlite	79.67% <78.26%> (-0.01%)	⬇️
unit	50.60% <69.56%> (+0.35%)	⬆️

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

Impacted Files	Coverage Δ
...hart-pivot-table/src/react-pivottable/utilities.js	0.00% <0.00%> (ø)
...frontend/src/components/DatabaseSelector/index.tsx	88.88% <ø> (ø)
...et-frontend/src/components/TableSelector/index.tsx	76.08% <ø> (ø)
...et-frontend/src/dashboard/actions/sliceEntities.js	74.28% <ø> (ø)
...t-frontend/src/filters/components/GroupBy/types.ts	100.00% <ø> (ø)
...rontend/src/filters/components/TimeColumn/types.ts	100.00% <ø> (ø)
...frontend/src/filters/components/TimeGrain/types.ts	100.00% <ø> (ø)
...frontend/src/SqlLab/components/ResultSet/index.tsx	50.68% <20.00%> (-0.71%)	⬇️
superset/models/helpers.py	40.78% <20.00%> (ø)
...rontend/src/components/ListView/Filters/Select.tsx	52.38% <33.33%> (-2.62%)	⬇️
... and 24 more

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[eschutho]

@betodealmeida I tested this locally and it pip install -e . doesn't pick up the entry points, only python setup.py install.

[betodealmeida]

@betodealmeida I tested this locally and it pip install -e . doesn't pick up the entry points, only python setup.py install.

Oh, that's weird... they should both pick them up.

[eschutho]

@betodealmeida and I worked through this and found that pip install -e . was working, but I just needed to point the entry point to the class differently. This is ready for review.