Build "promote" a WorkshopIdea following the StoryIdea pattern #518
Description
WorkshopIdeas are submitted by Users, and may or may not become Workshops
We want admins to be able to "promote" a WorkshopIdea to a Workshop, via url params
Follow the pattern established by StoryIdea form -> Story form, so the same feature is available for WorkshopIdeas
(the pattern is essentially adding url params to the "Promote" button, which is a new_workshop_path button and the Workshop form needs to default to params sent or f.object values)
