Your Godot version:
4.2

Issue description:
As someone new to godot, I have no clue on how to use renderingdevice for rendering after reading trough the documentation.
I have essentially these things that I'd like to learn from documentation:

• A minimal example.
• Can I use objects that are in scenes for rendering device?
• Can a rendering device coexist with rendering server?
• Can I access Gdshaders with rendering device?
• Can I use things like subviewports and cameras?

I have understanding of opengl and a surface level understanding of vulkan, but the real problem for me is how does this fit into godots existing systems.

I've also seen that, usage of rendering device will be required for rendering hooks in godot 4.3, so it would be nice to have that info for those as well.

URL to the documentation page (if already existing):
https://docs.godotengine.org/en/latest/classes/class_renderingdevice.html#class-renderingdevice-method-buffer-get-data