Diagnostics Module: Add health check that validates any Azure MFA auth certs

[bongiovimatthew-microsoft]

If a customer is using Azure MFA with ADFS, they configure an auth cert per ADFS node that gets used for authenticating that ADFS node to the Azure MFA server. (Details here).

It would be good to validate these certs, and also ensure that there is one per every node in the farm.