sendEnvelope
abstract suspend fun sendEnvelope(conversationId: ConversationId, envelope: MessageEnvelope, messageTarget: MessageTarget): Either<CoreFailure, MessageSent>
Send a Proteus MessageEnvelope to the given conversationId.
Return
Either.Right with the server date time in case of success
Either.Left of a ProteusSendMessageFailure if the server rejected the message
Either.Left of other CoreFailure for more generic cases