[Feature Request] Manual Workflow Trigger (Custom Field?)

Description

It would be very useful being able to manually trigger a workflow inside a specific document's view.

Not sure what the best option for this would be, but I think a pretty flexible solution would be having a kind of "button" custom field and a corresponding workflow trigger that gets called when that button is pressed.
That way we can define multiple buttons for different workflows and only assign the relevant buttons to each document.