[REST API] Get all users on all DSNs in a single paginate call

In order to get the USERS on the DSN, the developer needs to call the following endpoint:

https://learn.microsoft.com/en-us/rest/api/power-bi/gateways/get-datasource-users

However, that works only DSN on DSN basis. We have around 1000 dsns so daily we would have to call that endpoint 1000 times.

Add the new endpoint into the ADMIN API that works similarly as https://learn.microsoft.com/en-us/rest/api/power-bi/admin/groups-get-group-as-admin so it would be:

• single call
• paginated
• expandable for users via $expand property