Add Audience as an alias to TenantId.

[peombwa]

This PR closes #497 by:

• Adding -Audience as an alias to -TenantId. This allows customers to specify the sign-in audience they want to connect to. Also, TenantId and Audience are mutually exclusive and cannot be used together. See https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-client-application-configuration#authority.
• Updating Invalid_Scope error message by adding Please retry by specifying a sign-in -Audience or -TenantId to Connect-MgGraph. e.g., Connect-MgGraph -Audience 'organizations' -Scopes 'YOUR_SCOPES' -UseDeviceAuthentication. as a suggestion that can be used to resolve the error. When using device code flow, MSAL validates the provided scopes to see if they can be consented to using common audience (default audience). An Invalid_Scope error is thrown if the audience can't consent to the provided scope.

Proposal

Ref - https://docs.microsoft.com/en-us/azure/active-directory/develop/reference-aadsts-error-codes#aadsts-error-codes.