Add Scopes validation for ClientCredentials authentication

[ceciliaavila]

Description

This PR adds a validation for the Scopes setting, as at least one scope is required in the list for ClientCredentials authentication.
It also adds a new unit test to cover this case.

Detailed Changes

• Added new validation in the GetAccessTokenAsync method of the MsalAuth class.
• Added a condition to avoid NullReferenceExceptions when there are no Scopes in the settings in the ResolveScopesList method.
• Added a unit tests to cover the new validation in MsalAuthTests.

Testing

These images show the new exception thrown when the Scopes are not part of the settings and the new test passing.

[ceciliaavila]

/promoted 85