Fix: Add getAvailableValues for enum to Postgres parser;

[rokmohar]

This enables the Postgres parser to load available enum values for user defined types; This solves issue with filters for enum values. The error happened becuase of ilike comparison on custom data type for enum.

[BlackRockSoul]

Currently missing the col.udt_name on line 139-144

And I don't know the purpose of marking it as mixed here, but it works perfectly with just string

Thanks anyway, will make a local patch for myself