Slack webhooks should be configurable on the Canary object level

[alaqelsplk]

Our organization has a lot of teams so Canary alerts through slack would be hard to find in a single channel for the org. A good long term feature would be to have per-canary Slack channel options so that slack messages can be routed to specific channels for the team that owns that service.

[stefanprodan]

One option would be to use a Slack bot instead of a webhook since a bot can be invited to multiple channels. In the canary definition you would add a Slack channel and the Slack token could be a secret mounted as env var in Flagger's pod.