Construct a render graph from data

mstr from discords [raises](https://discord.com/channels/691052431525675048/743663924229963868/813334399319932970) some of the difficulties of modifying the default render graph that bevy ships. And some suggestions are raised.

Long term there is a vision to have a render graph editor. Before that can happen there needs to exist some kind of serialized data structure that can be deserialized and constructed into a RenderGraph.

This issue exists to track some of the work that would need to enable constructing a RenderGraph from data.

My current thinking is that as a first pass we could try to replicate the functionality of `BaseRenderGraphBuilder` with something that gets constructed from a Ron file. See how it feels and decide where to take it from there.