[TECH-263] Allow command handlers to consume query handlers

[asimmon]

The rule GMDTR09 "Handlers should not call other handlers" is a bit too strict right now. It prevent command handlers from consuming query handlers. This PR allows this behavior.

Added more tests to validate the following behaviors:

• Notification handlers can be called from any handler
• Command handlers can call query handlers
• Command handlers cannot call other command handlers
• Query handlers cannot call command handlers
• Query handlers cannot call other query handlers