Report Usage Metrics Report: add Domain column to Users table

[fred1]

For the metrics report and data model, add a Domain column to the Users table. This would be a column that extracts everything after the @ sign in the UserPrincipalName email address. This addition would make it possible to slice the data by email domain, which would be super helpful in comparing internal vs. guest users (e.g. with Azure B2B guest users or other cases).