document: canton should only available for switzerland

The canton field should only be available when the country 'Switzerland'
was selected in the provisionActitivy country field.

Closes #1285

Co-Authored-by: Renaud Michotte <renaud.michotte@gmail.com>

rero_ils/jsonschemas/common/cantons-v0.0.1.json

@@ -139,7 +139,8 @@
       ],
       "templateOptions": {
         "cssClass": "col-lg-4"
-      }
+      },
+      "hideExpression": "field.parent.model.country !== 'sz'"
     }
   }
 }