Better validation of connector prerequisities

Some connectors `#validate` method check quite precisely, if the environment is setup correctly. The postgres connector for example validates grants and roles etc to run in different local and cloud based environments.
All connectors should check their requirements (as good as possible) in `#validate` to ensure they are able to run properly.

This inlcudes:

• roles, grants (available replication slots or the right to create slot etc)
• access to specific schemas/tablespaces, database parameters
• all include / exclude list entries should report the matching tables/collections or the number of matching tables/collections