CloudEvents format for messages

[oncicaradupopovici]

Adopt the CNCF Cloud events standard for messaging

https://cloudevents.io/ https://github.com/cloudevents/sdk-csharp

Proposed solution

FeatureFlag: CloudEvents compatible Keep MessagingEnvelope; Add ToCloudEvent FromCloudEvent functions Modify MessagingTransport to receive/return MessagingEnvelope instead of ReceiveContext/ SendContext Add custom ProtocolBinding and Formatter for legacy message format or just use exiting code. Use existing or develop Formatter/ ProtocolBinding for Stan. For Rusi Transport, just add enough information related to Cloud Events and let Rusi do the envelope.