fix: move dynamic schema out of base Postgres class

[hughhhh]

SUMMARY

Moving specific logic to PostgresEngineSpec to allow other specs (Redshift) to have more control over how we create the engine since the options keys are not the same for individuals

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

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 #23868 (3aee03c) into master (594d3e0) will not change coverage.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##           master   #23868   +/-   ##
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  Coverage   68.11%   68.11%           
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  Files        1938     1938           
  Lines       74972    74972           
  Branches     8141     8141           
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  Hits        51067    51067           
  Misses      21826    21826           
  Partials     2079     2079           

Flag	Coverage Δ
hive	53.01% <27.77%> (ø)
mysql	78.80% <61.11%> (ø)
postgres	78.88% <61.11%> (ø)
presto	52.93% <27.77%> (ø)
python	82.67% <100.00%> (ø)
sqlite	77.39% <61.11%> (ø)
unit	52.81% <94.44%> (ø)

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Impacted Files	Coverage Δ
superset/db_engine_specs/postgres.py	97.12% <100.00%> (ø)

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[betodealmeida]

I think we can actually get rid of the get_schema_from_engine_params method here, since Redshift doesn't support passing search_path as far as I could see.

[eschutho]

@hughhhh or @betodealmeida Netezza, snowflake, hana and vertica also are based from the PostgresBaseEngineSpec. Have we tested how this change impacts those dbs?

[hughhhh]

@hughhhh or @betodealmeida Netezza, snowflake, hana and vertica also are based from the PostgresBaseEngineSpec. Have we tested how this change impacts those dbs?

this is basically a revert on what current functionality, instead of having supports_dynamic_schema = True in the base class instead we moved this functionality to live only in the specific engine specs snowflake example

i can write a test to verify this