Add basic tag position to fire_hydrant (#418)

As per osm wiki, emergency=fire_hydrant should have the
fire_hydrant:position tag.
https://wiki.openstreetmap.org/wiki/Tag:emergency%3Dfire_hydrant

data/fields/fire_hydrant/position.json

@@ -0,0 +1,15 @@
+{
+    "key": "fire_hydrant:position",
+    "type": "combo",
+    "label": "Position",
+    "strings": {
+        "options": {
+            "green": "Green/Grass",
+            "lane": "Road Lane",
+            "sidewalk": "Sidewalk",
+            "parking_lot": "Parking Lot"
+        }
+    },
+    "autoSuggestions": false,
+    "customValues": false
+}