Rename "Interface Endpoints" -> "Private Endpoints"

[rupalivohra]

Is your feature request related to a problem? Please describe.
We have received feedback from the LT to rebrand Interface Endpoints to Private Endpoints

Describe the solution you'd like
All of the same APIs previously planned for Interface Endpoints, but now for Private Endpoints. For now, this will only impact the GET API (since write ops have not been published).

Describe alternatives you've considered
n/a

Additional context
Email chain so far w/ Travis:

From: Travis Prescott
Sent: Wednesday, October 10, 2018 8:19 AM
To: Rupali Vohra rupaliv@microsoft.com
Cc: Mario Lopez malop@microsoft.com; Sumeet Mittal Sumeet.Mittal@microsoft.com; Ajinkya Potdar ajpotd@microsoft.com
Subject: RE: Naming change for Interface Endpoints

You’ll need to post a CLI issue, and it will be a breaking change for the CLI so it will not be able to go in immediately.

From: Rupali Vohra
Sent: Tuesday, October 9, 2018 7:40 PM
To: Travis Prescott trpresco@microsoft.com
Cc: Mario Lopez malop@microsoft.com; Sumeet Mittal Sumeet.Mittal@microsoft.com; Ajinkya Potdar ajpotd@microsoft.com
Subject: Naming change for Interface Endpoints

Hi Travis,
The feature we were targeting for Ignite, Interface Endpoints, did not have a public announcement. We’ve since received feedback that the name needs to be changed from “Interface Endpoint” to “Private Endpoint.”

We’re still working on the changes in APIs on the NRP-side, but I wanted to let you know that this change is coming your way. Let me know if you prefer creation of an Issue on GitHub.

Best,
Rupali