Subscribe to issue status updates

[cbjrobertson]

Is your feature request related to a problem? Please describe.
I'm frustrated by the fact I don't seem to be able to subscribe to issue status updates.

Describe the solution you'd like
As issues progress from "to do" -> "in progress" -> "under review", I'd like the slack channel to be notified. This could be implemented with github subscribe org/repo issue-status-updates command or something similar.

Describe alternatives you've considered
If there are alternatives already available in the application, I'm not aware of them.