Slack connector just dumps raw JSON into the Slack message—improve message format

[merlin-quix]

I'm trying to pipe an RSS feed into Slack from the RSS Source (without the RSS filter transformation) but it seems to dump a whole much of JSON into the Slack message rather than give it a human readable format.

I would expect an environment variable to let me define where to get the text of the Slack message from the payload but there's only a variable for the webhook URL: