Add @Attachment byte[] interface #485

I'm submitting a ...

• feature request

What is the current behavior?

Currently @Attachment can only be used with byte[] and String return types.

What is the expected behavior?

I propose adding an interface AttachmentBytes as another return type understood by @Attachment annotation:

public interface AttachmentBytes {
    byte[] attachmentBytes();
}

What is the motivation / use case for changing the behavior?

I would like to use a custom return type other than byte[] and String so that I do not need to convert to a raw type every time I use @Attachment