Make updateCameraTag default true

[De-Panther]

The WebXRCamera.updateCameraTag decides if the cameras objects tag will be updated when switching XR modes.
Some Interaction packages, like Unity XR Interaction Toolkit relay on the Camera.Main (which looks for active Camera components with MainCamera tag).

I don't like to magically change values without developers knowledge, but it seems like this is now the expected behavior, as lots of projects want to use such packages.

Would solve issues like the one mentioned in #438 (comment)

• Change updateCameraTag to true.
• Change the value in the samples prefabs.
• Add more info about this variable in code.
• Update the LLM file "Common Issues & Notes" to include this.
• Update the CHANGELOG files.