add "unleashed" as value for dog tag field

and limit offered values of `dog` field on dog-specific features to just =leashed`/`unleashed`: `no` does generally not make sense on these, and `yes`/`designated` is already implied by the primary tag.

data/fields/dog.json

@@ -6,6 +6,7 @@
         "options": {
             "yes": "Allowed",
             "leashed": "Leashed Only",
+            "unleashed": "Leashes Not Required",
             "no": "Not Allowed"
         }
     },

data/fields/dog_yes.json

@@ -0,0 +1,12 @@
+{
+    "key": "dog",
+    "type": "combo",
+    "label": "{dog}",
+    "options": [
+        "leashed",
+        "unleashed"
+    ],
+    "stringsCrossReference": "{dog}",
+    "autoSuggestions": false,
+    "customValues": false
+}