Slack: a message to a person, or to a channel of the team's.
channels: [slack: {Chime.Channels.Slack, token: System.fetch_env!("SLACK_BOT_TOKEN")}]With a bot's :token, Chime posts with chat.postMessage to the
person's Slack id (or a channel's), from the recipient's data
(data.slack, or to: {:data, :slack_id}), or to one to: "#alerts" for everyone. Without a token, the address is an incoming
webhook's URL (to: "https://hooks.slack.com/services/...", or each
person's in their data).
It says the notifier's slack/3 when it has one (a text, or a map of
:title, :body, :url), else the feed's words, with the link that
reads the notification. Options: :token, :to, :req_options.