Add filter behavior explicitly

Author: benjie

src/PgConnectionArgFilterPlugin.ts

@@ -80,6 +80,10 @@ export const PgConnectionArgFilterPlugin: GraphileConfig.Plugin = {
           description: "Can this function be filtered?",
           entities: ["pgResource"],
         },
+        filter: {
+          description: "Can this table be filtered?",
+          entities: ["pgResource"],
+        },
       },
     },