This adds a webhook that can be used to interpret standard Slack
payloads. Since there are a ton of existing Slack integrations out
there, having a webhook which can accept standard Slack payloads can
significantly ease transition pains. Obviously this can't do everything
that Slack payloads can (particularly WRT their widgets/interactions),
but we can ingest text and parse out multi-block payloads into a message
relatively reasonably.
Chris Heald