Enable advanced monitoring for SQLServer & Postgres.

[anjagruenheid]

This PR introduces advanced monitoring (per query and system stats) for SQL Server and Postgres. Anyone currently using monitoring will not be impacted as advanced monitoring will need to be enabled with a new CL option (mt=advanced).

In essence, this code addition allows users to run queries against system tables (SQL Server) or plugins (Postgres) which allows us to extract system and query usage statistics while benchmarking (query plans, query text, pattern execution counts, cache hits etc.).