invite: add button for invite someone to collaborate on a draft

spec/controllers/invites_controller_spec.rb

@@ -69,11 +69,16 @@ describe InvitesController, type: :controller do
 
       context 'when user has access to dossier' do
         before do
+          request.env["HTTP_REFERER"] = "/dossiers/#{dossier.id}/modifier"
           dossier.update(user: signed_in_profile)
         end
 
         it { expect { subject }.to change(InviteUser, :count).by(1) }
 
+        it "redirects to the previous URL" do
+          expect(subject).to redirect_to("/dossiers/#{dossier.id}/modifier")
+        end
+
         context 'when email is assign to an user' do
           let! (:user_invite) { create(:user, email: email) }