Currently, when I want to use a uuid as the primary key, I need to
declare as:

public class User {
@Id
public UUID id;
}

It works well, but sometimes not convenient. For example, if I want to
dump a user instance to yaml, or json, the id can't be converted,
because they don't know how to convert UUID

I hope ebean can provide an annotation, such as @UUID(or other), then
we can use String as the type:

public class User {
@Id
@UUID
public String id;
}

Is it possible?