Allow ConfigDataLoader & EnvironmentPostProcessor to opt-out in AOT refreshed contexts

[snicoll]

Preparing the Environment in a Spring Boot application have various forms depending on what's on the classpath. This can trigger HTTP calls to remote config server for instance. Wavefront also negotiates an API token if none is found.

In the latter case, it's obviously wrong to do that at build-time as the API token will not be used as we're evaluating conditions and not instantiating beans. Having the ability to know that the environment is prepared for an Ahead-of-time context optimization will allows those components to react accordingly.