Custom PostgreSQL type mapping

PostgreSQL does have a fixed type OID assignments for all the built in types. Extensions will add custom OID that do not have a specific OID and can change according to the database instance.

We need to support such types and have the ability to provide a dynamic mapping so that custom types can be correctly encoded/decoded.

So basically we can

1. start by providing a OID <-> Codec table to the driver by the user (easy to do ?)
2. add an utils to build such table using SQL