Investigate and spike the required changes to support sending messages using the CloudEvents envelope format

[mauroservienti]

Currently, this package and NServiceBus Core only support receiving messages wrapped in a CloudEvents envelope. Functionalities like sending messages, replying to senders, or replying to the originator in Sagas are not supported.

The goal of this issue is to investigate the required changes to Core and this package, to introduce support for the following functionalities:

• Sending a CloudEvent, possibly allowing users to configure formats on a per-destination basis
• Replying, as in context.Reply, in the context of an incoming message, considering that the outgoing message should respect the incoming message format (e.g., if the incoming message is an NServiceBus message, the reply should use the same format, if it's a JSON structured CloudEvent, the reply should comply)
• ReplyToOriginator in Sagas, with all the same caveat of the reply logic and the additional issue that the format of the message that originally started the saga is not stored anywhere.
• Map the NServiceBus.EnclosedMessageTypes to the outgoing corresponding CloudEvent type-related property
• The reply must honor the source CloudEvent property