Provide a toggle to discard every queued run in one stack

It will be very helpful if there is a button on every stack’s page near Sync and Trigger to discard all queued runs in one stack. The context is that, sometimes during an incident, we merged a fix PR which is on the tip of master branch, but we need to discard every run before it and trigger a run on the tip of the master branch, and now we need to click every single run and call discard, which takes time a lot.