Theme(hailhydrant): add ref question (#1454)

assets/layers/hydrant/hydrant.json

@@ -574,6 +574,29 @@
         "es": "Diámetro de los acoplamientos: {couplings:diameters}"
       }
     },
+    {
+      "id": "ref",
+      "question": {
+        "en": "What is the reference number of this hydrant?",
+        "nl": "Wat is het referentienummer van deze brandkraan?"
+      },
+      "questionHint": {
+        "en": "This can usually be found on the hydrant or on a nearby sign.",
+        "nl": "Dit nummer is meestal te vinden op de brandkraan of op een nabijgelegen bord."
+      },
+      "freeform": {
+        "key": "ref",
+        "placeholder": {
+          "en": "Reference number of the hydrant",
+          "nl": "Referentienummer van de brandkraan"
+        },
+        "type": "string"
+      },
+      "render": {
+        "en": "Reference number: {ref}",
+        "nl": "Referentienummer: {ref}"
+      }
+    },
     "images"
   ],
   "allowMove": {