TMSS-528: enforce at least one station

SAS/TMSS/backend/src/tmss/tmssapp/schemas/common_schema_template-stations-1.json

@@ -68,13 +68,14 @@
         ]
       },
     "station_list":{
-      "default":[],
+      "default":["CS002"],
       "type":"array",
       "additionalItems":false,
       "additionalProperties":false,
       "items":{
         "$ref": "http://tmss.lofar.org/api/schemas/commonschematemplate/stations/1#/definitions/station"
       },
+      "minItems": 1,
       "uniqueItems":true
     },
     "max_number_of_missing_stations": {