Support microsoft/microsoft-graph:2.0

[radimvaculik]

https://github.com/microsoftgraph/msgraph-sdk-php/blob/dev/UPGRADING.md

[36864]

Gonna be honest here, I didn't expect version 2 to be released in my lifetime.
I am currently absolutely swamped and don't expect to have free time to implement whatever needs to be changed soon. Any help in the form of pull requests would be greatly appreciated.