TMSS-717: enforcing a minimum of one station in the list is too strict,...

TMSS-717: enforcing a minimum of one station in the list is too strict, sometimes an empty stationlist is ok.

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

@@ -73,7 +73,7 @@
       "items":{
         "$ref": "http://tmss.lofar.org/api/schemas/commonschematemplate/stations/1#/definitions/station"
       },
-      "minItems": 1,
+      "minItems": 0,
       "uniqueItems":true
     },
     "max_number_of_missing_stations": {