[GR-66791] Introduce SingletonTraits annotation.

[graalvmbot]

This PR adds the @SingletonTraits annotation, which we intend to be a replacement for the LayeredImageSingleton (and children) interfaces.

The benefits of switching to an annotation include:

1. it can directly label the singleton class with all relevant information - we don't have to worry about inheriting traits
2. it can be injected into 3rd party code

More details about the traits themselves can be found in the javadoc included as part of this PR