[17.0] crm_lead_to_task: Notify task assignees when the opportunity is lost

[max3903]

Is your feature request related to a problem?

When the lead is lost, the task assignees don't know about it.

Describe the solution you'd like

I would like a message to be posted automatically on the task chatter to notify the assignees/followers that the opportunity has been lost, so they stop working on it.

Describe alternatives you've considered

Sending an email. Changing the task to the closed stage.