Event bus streaming mockup

[vietj]

A refactoring that decouples a few things + framing introduction

• decouple the registration handlers from current interactions (e.g remove the reply handler knowledge from the registration handler)
• a registration handler now process generic frames
• a message is a frame
• clustering are responsible to send frames to peers very much like they are sending messages (which is now a specific frame)

Thanks to frames we keep existing interactions as well as allow new interactions to support bidi streaming. Very similar to TCP we have syn/fin frames between peers to control stream boundaries.

See also #4712 that does the same but keep the existing protocol using codecs to implement the protocol instead of adding frames.

[vietj]

@tsegismont FYI

[He-Pin]

Add an Enum FrameSource?