Support pluggable types for EndpointObjectMapper

[philwebb]

In order to create a health module we need to break the link between HealthComponent and OperationResponseBody. The main purpose of OperationResponseBody is to provide an association from a type to the EndpointObjectMapper.

I think we can add a new method on EndpointObjectMapper to provide that link.

[philwebb]

With the refactored health work we might be able to revert this.