Hope add email Fanout Triggers

[yswtrue]

[kodless]

@yswtrue Now after adding batch processing to Leek in version 0.5.5, I think of deprecating the slack fanout triggers and add a global HTTP webhook configuration per Leek application.

The events will be sent to an HTTP endpoint deployed on your infrastructure and then you can decide what to do with the received alerts (ie. fanout to email)

This will make the events processing faster because Leek agent will not have to wait for Leek API to fanout each event to slack/email and it will send them in batch to the webhook endpoint.