[Microsoft.DeviceUpdate] Added private Network RP API for Private Endpoint support (Azure#16396)

* Added internal Network RP model and API

* Fixed semantic validation error

* prettier run

* Added list operation for NRP-only proxy type

* Linter fixes

* Removed properties requirement

* Removed read-only flags

* Removing required from resources

* More required properties

* More c&p error fixes

* Added missing property definition for remote proxy

* Wrong place for provisioning state

* Rogue space

* Fixed an example

* Another rogue space

* Added internal note to descriptions

Author: darkoa-msft