Fixed type mismatch in design management queries

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/11056

ee/app/assets/javascripts/design_management/queries/allDesigns.graphql

 #import "./designListFragment.graphql"
 
-query allDesigns($fullPath: ID!, $iid: ID!) {
+query allDesigns($fullPath: ID!, $iid: String!) {
   project(fullPath: $fullPath) {
     issue(iid: $iid) {
       designs {

ee/app/assets/javascripts/design_management/queries/permissions.graphql

-query permissions($fullPath: ID!, $iid: ID!) {
+query permissions($fullPath: ID!, $iid: String!) {
   project(fullPath: $fullPath) {
     issue(iid: $iid) {
       userPermissions {