Description of the feature request
Hey! When sending messages to Slack, you are able to specify a thread_ts parameter that matches the ts of a previously sent message in order to send the new message as a reply in a thread. Additionally, you can also specify reply_broadcast (boolean) to optionally send the message to the channel as well as in the thread.
For the reasons detailed in the Use Case below, it would be great for the Slack step to support this.
API documentation here: chat.postMessage method | Slack
Use case / for what or how I would use it
We have a Slack bot that operates outside of Bitrise used to trigger builds from the Slack interface, when our builds run, the workflows often send at least a couple of Slack messages (one about the build starting, another about the result with links to artefacts etc) but this can mean that our deploy channel often gets noisy.
To help reduce noise in the main channel, it would be great if Bitrise could send the followup messages in the thread from the original trigger message. In addition, since failures are also important. It would be good if errors could be broadcast back to the original channel.
Because we first send an initial Slack message in an outside tool, we already have the ts of the original message, which is great but others might not have this value, so it might also be worthwhile for the step to return the origin messages ts value as an output so that it can be passed into subsequent step calls.
