Update type for paymentModel

Author: Raphael-Gazzotti

schemas/miscellaneous/accessibility.schema.tpl.json

@@ -33,6 +33,9 @@
       ]
     },
     "paymentModel": {
+      "type": "array",
+      "minItems": 1,
+      "uniqueItems": true,
       "_instruction": "Add all relevant payment model types indicating how access costs are determined. If no payment is requires, select zero-cost payment model.",
       "_linkedTypes": [
         "controlledTerms:PaymentModelType"