Add Slack notification

[guibranco]

Is there an existing issue for this?

• [X] I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

I would like to have Slack notifications via API key and custom channel URL

Describe the solution you'd like

Like the email notification, add a provider for Slack notification.

Sending messages using Incoming Webhooks

Additional context

https://api.slack.com/best-practices/blueprints/actionable-notifications

[berkansasmaz]

Thank you for your feature request, I am adding it to the backlog and I will try to deal with it as soon as possible.