Can not easily opt out of rendering UI on a camera

## Bevy version 0.14.2

## What you did
I want to provide users a plugin to debug their UI. Think chrome dev tools for bevy UI.
I also want to use gizmos to add some guides on where the currently inspected element is positioned on screen.
Gizmos are rendering behind the UI by default.
If I want the gizmos to render on top, I need to add an extra camera for my plugin with a higher Order.
The DefaultUiCamera System param defaults to the camera with the highest order.

I can't provide a plugin that renders gizmos on top of the users UI, as there is a high chance that the plugin's camera will be the default ui camera.

## What went wrong

If a plugin spawns a camera with a higher than default order, there is a big chance it will be the DefaultUiCamera.

- what were you expecting?
I want to opt out of any UI not explicitly targeting this camera.

- what actually happened?
I need to request the user to set the IsDefaultUiCamera on there preferred camera.

## Additional information

Related discussion on #ui-dev in discord:https://discord.com/channels/691052431525675048/743663673393938453/1303324220608217169

Start by tracing the DefaultUiCamera system parameter, IsDefaultUiCamera, camera order, and the gizmos/UI rendering behavior described in the issue. Define and validate a way for a plugin camera to render gizmos over the user's UI without becoming the default UI camera, while preserving explicit camera targeting.

Written by the indexing model from the issue text.