Avoid or document the pitfalls of the bootstrap context

From what I've seen, the separate bootstrap context and its consequences continue to surprise users. The latest example is with disabling auto-configuration of Reactor's debug agent. I think it would be an improvement if users didn't have to know so much about the bootstrap context and its presence didn't require some configuration to move from application.yaml to bootstrap.yaml.

I can't recall the history of the context, but I wonder if it's still needed now that we have the environment post-processor extension point. If it is still needed, I wonder if it could be made a bit more "closed world" so that extensions that are really aimed at the main application context are not picked up by the bootstrap context. Failing that, documenting the problem and the need to move some configuration properties would help I think.

Start by reviewing the bootstrap context behavior and the linked Reactor debug-agent example, then compare how configuration is loaded from application.yaml versus bootstrap.yaml. Determine whether the bootstrap context is still needed or whether its effects should instead be constrained or documented; done means one of those directions is agreed and its user-facing consequences are addressed.