arista/alert.v1: Add user_principal_name for MsGraphSendMailSettings

The rAPI is missing a required field user_principal_name, that is
necessary to call the MS Graph send mail API using a client
credential OAuth flow.

[GENERATED_COMMIT]

Change-Id: I0b93e5226ccf478582a855763b123fa8ce0da702

Author: Arista-Jenkins