make public storage and direct upload optional

app/javascript/submission_form/image_step.vue

@@ -30,6 +30,7 @@
       :message="`Upload ${field.name || 'Image'}${field.required ? '' : ' (optional)'}`"
       :submitter-slug="submitterSlug"
       :accept="'image/*'"
+      :is-direct-upload="isDirectUpload"
       @upload="onImageUpload"
     />
   </div>
@@ -50,6 +51,11 @@ export default {
       type: Object,
       required: true
     },
+    isDirectUpload: {
+      type: Boolean,
+      required: true,
+      default: false
+    },
     submitterSlug: {
       type: String,
       required: true