* Slack: Add bot/user token support, correct thread_ts support
Add support for user/bot/application tokens (and Slack WebAPI).
Fix input type for thread_id, which needs to be string.
Return thread_ts/thread_id when user/bot tokens are used, so they can be reused later
* Slack: Add changelog fragment, fix YAML syntax
Co-authored-by: Middleton, Michal <Michal.Middleton@concur.com>
