Add option to specify system tables

[hfhbd]

Each database has unique system tables containing system information. At the moment sql-psi does not know about these tables so referrencing to these tables fails with No table found with name.

Sample: DB2 requires a FROM clause, so you have to use the SYSIBM.SYSDUMMY1 for simple selects: SELECT TIME_STAMP FROM SYSIBM.SYSDUMMY1. Oracle provides a similar dual table.

Same use case for system catalog with PostgreSQL: https://www.postgresql.org/docs/current/catalogs.html