Add client for managing Connected Organizations in entitlement management

[askew]

This is (currently) draft change to add the client needed to manage Connected Organizations in entitlement management according to the API specification:

https://docs.microsoft.com/graph/api/resources/connectedorganization?view=graph-rest-1.0

It fixes Issue #155

[manicminer]

Thanks for the PR @askew. I'll look at getting the test environment set up with a second tenant and will review once I've been able to try it out.

[kaovd]

Hi @manicminer have you managed to sort a test environment for this yet?