Add PostgresConnection based SQLDatabase

[ptoffy]

If we have a PostgresConnection (which we'll do after vapor/fluent-postgres-driver#227) we can use that as SQLDatabase without having to go through PostgresDatabase

[codecov]

Codecov Report

❌ Patch coverage is 95.12195% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.35%. Comparing base (11d6910) to head (b6ff209).

Files with missing lines	Patch %	Lines
...urces/PostgresKit/PostgresConnectionDatabase.swift	95.12%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #284      +/-   ##
==========================================
+ Coverage   45.90%   46.35%   +0.44%     
==========================================
  Files          13       14       +1     
  Lines         891      932      +41     
==========================================
+ Hits          409      432      +23     
- Misses        482      500      +18     

Files with missing lines	Coverage Δ
...urces/PostgresKit/PostgresConnectionDatabase.swift	95.12% <95.12%> (ø)

... and 1 file with indirect coverage changes

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[0xTim]

Lets pull in the one from Swift Log for testing