Use `content_id` in routes
Use `content_id` in routes

When Rails constructs URLs it provides the id of the object as
`params[:id]`. In order to allow us to refer to it as
`params[:content_id]` (as that's what it really is), this commit
adds `param: :content_id` to the resourceful route.

alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher