Challenge: Implement a Custom Exception

In this task, you will define a custom exception class and use it to handle invalid user input in a registration form scenario. This will help you practice creating your own exception types and using them to manage errors in a more meaningful way.

• Define a custom exception class named InvalidRegistrationException that extends the built-in Exception class.
• Implement the validateRegistration function so that it throws an InvalidRegistrationException if the username is empty.
• Make the function throw an InvalidRegistrationException if the password is less than 6 characters long.
• If both checks pass, the function should return a success message containing the username.