OTB does not support anymore classes which use pqxx in version 4.0:

Classes removed in OTBv4 are:
        - PostGISConnectionImplementation
        - PostGISTable
        - GISTableFunction
        - PostGISCreateTableTransactor
        - PostGISFromStringTransactor
        - PostGISQueryTransactor
        - TransactorGISTableFunction

You can still access to these classes, related tests and examples in OTB 3.20.