feat: add placeholder table/functions for pg_description queries

[sunng87]

This is to address dbeaver query:

SELECT t.oid,t.*,c.relkind,format_type(nullif(t.typbasetype, 0), t.typtypmod) as base_type_name, d.description
    FROM pg_catalog.pg_type t
    LEFT OUTER JOIN pg_catalog.pg_type et ON et.oid=t.typelem
    LEFT OUTER JOIN pg_catalog.pg_class c ON c.oid=t.typrelid
    LEFT OUTER JOIN pg_catalog.pg_description d ON t.oid=d.objoid
    WHERE t.typname IS NOT NULL
    AND (c.relkind IS NULL OR c.relkind = 'c') AND (et.typcategory IS NULL OR et.typcategory <> 'C')

But we are still blocked by this t.oid, t.*, which will be rejected by datafusion, say:

Projections require unique expression names but the expression "t.oid" at position 0 and "t.oid" at position 1 have the same name. Consider aliasing ("AS") one of them.