ConnectionApproval spawn by prefabhash unusable

[LukeStampfli]

Describe the bug
The ConnectionApproval callback allows to pass back a prefab hash to spawn a specific prefab as the player object for the connection player. This is no longer possible by code since prefabs don't have a prefabHash anymore and GlobalObjectId is internal.

To Reproduce
Steps to reproduce the behavior:

1. Override the connection approval callback in the NetworkManager and try spawning a different player object with it.

Actual outcome
It's not possible to do.

Expected outcome
It should work or be removed

Environment (please complete the following information):

• OS: Windows 10
• Unity Version: 2020.3.12f1
• Netcode Version: 1.0.0-pre.2

[NoelStephensUnity]

This is a runtime only issue that requires the connection approval callback accepting a Network Prefab or that the GlobalObjectIdHash value is exposed as public read only and internally set.
MTT-1645

[RikuTheFuffs]

@NoelStephensUnity Now that this is merged, is this issue resolved?