Add ability to create bean default transformer

[Idane]

Currently, bean transformers in Spring can not be registered as default.

1. For annotated transformers, we could add a @DefaultMappingTransformer annotation which will register the transformer as default
2. For transformers declared as beans from JavaConfig/XML, maybe we could add a construct similar to FilterRegistration, where additional information on the transformer is defined, could also utilize the existing TransformerRegistration for this purpose