can_push
The v3 API documentation claims that `can_push` is supported when adding a deploy_key. https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/deploy_keys.md#add-deploy-key Here we make good on this promise by adding `can_push` as an optional parameter so grape can route it. This was copied from the v4 API.
requirements: { id: %r{[^/]+} }
Signed-off-by: Rémy Coutable <remy@rymai.me>