Do not use the message from the underlying error

[Widcket]

Changes

This PR changes the error message logic for CredentialsManagerError and AuthenticationError so that it will not automatically return the error message from the underlying error if there is one, because the developer is expected to handle the underlying error anyway, and having both the error and underlying error have the same message could be confusing.

Testing

• This change adds unit test coverage
• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines
• All existing and new tests complete without errors
• All active GitHub checks have passed