Fixes https://github.com/spring-projects/spring-integration/issues/3994 Essentially, migrate those hints from Spring Boot Actuator: an `IntegrationGraphServer` can be used without Spring Boot * Introduce `IntegrationGraphRuntimeHints` - implementation of `RuntimeHintsRegistrar` to register reflection hints for `Graph` and top-level `IntegrationNode` types. * Use `@ImportRuntimeHints` on the `IntegrationGraphServer` to make those hints conditional.