Add CameraSettingsManager to the MRTK XR Rig

[shaynie]

Add the 'Unknown' display type and default to 'Unknown' when there is no running XRDisplaySubsystem running. Add CameraSettingsManager to the MRTK XR Rig prefab

Overview

Changes

• Fixes: Determine if CameraSettingsManager is still needed in MRTK3 #11591

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[AMollis]

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