fix warning for no credential scopes and BearerTokenCredentialPolicy

[iscai-msft]

current error is

You have used the --add-crede
ntial flag but not the --credential-scopes flag while generating non-management plane code. This is not recommend because it forces
the customer to pass credential scopes through kwargs if they want to authenticate.

Replacce references to add-credential to bearerTokeNCcredentailPolicy