UX: Can't see error message about deploy key without scrolling to the top of the page

As reported in https://gitlab.com/gitlab-com/support-forum/issues/4036, to reproduce:

  1. Go to :project/settings/repository and add an existing SSH key to the Deploy Key.
  2. You then see this:

image

  1. You have to scroll to the top of the page to see the error:

image

I think this is happening because the submit reloads the same page, but #js-deploy-keys-settings is still the anchor. We should probably scroll back to the top of the page if there is a flash content.