Add ability to describe undelivered messages in sequence diagram

[Mingun]

Proposal

Some diagram software allows you to break arrow to indicate, that message was not delivered, for example, due to connection lost in network communication diagram. It would be great if Mermaid can support this.

Example

The proposed syntax for the feature may be this (the x symbol at end of link):

ATM ->> Host: Transaction request
Host ->x ATM: Response (undelivered)

It should be rendered like this:

ATM    Host
 |----->|
 | x----|
ATM    Host

Screenshots

No response