Document user roles/grants necessary for Db2 connector user accounts

The Db2 connector documentation isn't very clear about what specific user roles are needed and ideally, we should clarify this in the documentation to avoid any potential questions about situations where users may want to limit the visibility of the connector user account to only the necessary database bits.

According to an exchange with Luis, the connector user only requires read access for the tables that are being captured and the corresponding CDC tables. The test suite uses the same user that creates the tables for simplicity, but that's not a requirement. We may want to make sure that we also illustrate this within the examples to be clear as well.