New API to allow starting a new conversation

[mikeminutillo]

An API to trigger a new conversation. This can be useful in a few scenarios:

• A long-running saga based scheduler.
• An integration handler that loads records and then starts a new process for each record.

var sendOptions = new SendOptions();
sendOptions.StartNewConversation();
// or
// sendOptions.StartNewConversation("CustomConversationId/"+Guid.NewGuid());
await context.Send(new PlaceOrder(), sendOptions);

This will override the conversation Id for an outgoing message.

• If a conversation id is supplied, use it
• If no conversation id is supplied, generate one using the configured conversation id strategy
• If a new conversation is started in the context of a message hander, the original conversation id is stored in a new NServiceBus.PreviousConversationId header.
• If a new conversation is started using this API, any attempt to set the ConversationId header manually causes an exception.

[mikeminutillo]

Raised a couple of issues in ServiceInsight to:

• Show link to triggering conversation
• Show link to new conversations