Merge pull request #4938 from DSpace/backport-4937-to-dspace-7_x

[Port dspace-7_x] Add the missing ADD policy action to the resource policy form

Author: tdonohue

src/app/shared/resource-policies/form/resource-policy-form.model.ts

@@ -39,6 +39,10 @@ const policyActionList: DynamicFormOptionConfig<any>[] = [
     label: ActionType.WRITE.toString(),
     value: ActionType.WRITE
   },
+  {
+    label: ActionType.ADD.toString(),
+    value: ActionType.ADD,
+  },
   {
     label: ActionType.REMOVE.toString(),
     value: ActionType.REMOVE