`az ad app owner add` appears to rely on deprecated `graph.windows.net`

We've been struggling to get a Service Principal, which is an Owner on an App Registration, to add other Owners to that App Registration.

The Service Principal has an admin-consented AppRoleAssignment to Microsoft Graph's `Application.ReadWrite.OwnedBy`. However, when running `az ad app owner add` we were faced with an insufficient permissions error.

We have resolved that error by creating an admin-consented AppRoleAssignment to **Windows AAD Graph**'s `Application.ReadWrite.OwnedBy` too. We can't do that through the portal anymore, as that control is grey'd out because the [AAD Graph has been deprecated](https://techcommunity.microsoft.com/t5/azure-active-directory-identity/update-your-applications-to-use-microsoft-authentication-library/ba-p/1257363) and goes out of support in June 2022.

This command seems to be quietly falling out of support. In the short term, could the documentation be updated to inform users that they will have to have Windows Graph permissions to make it work?