Allow Webhooks to post to Reply Threads
At the moment, the "comment" value for response_type will only trigger for the triggering message, even if that message is part of a thread. Maybe a value of "thread" can tell it to reply in the thread rather than creating another thread just to respond to the trigger message.
Just wondering: There is also the open request [Ability to Reply to Message with Webhook](https://mattermost.uservoice.com/forums/306457-general/suggestions/31914865-ability-to-reply-to-message-with-webhook). Is this essentially the same one as this request and could these be merged?
Incomming Webhooks, that can open or send into a thread, would greatly improve clarity in channel history.
Example: a script send a webhook-based message on "start", then on "finish".