Previously Microsoft Graph only worked for the default Azure
deployment. However, there are currently three other national clouds
supported in Azure
(https://docs.microsoft.com/en-us/graph/deployments).

This update adds support for the `graph_endpoint` and
`azure_ad_endpoint` to enable support for these alternative Azure
deployments.

This pulls in https://github.com/tpitale/mail_room/pull/140 to address
https://github.com/tpitale/mail_room/issues/139.

Changelog: changed