Add support for onError RFC (#2694)

Author: benjie

.changeset/ninety-animals-ring.md

@@ -0,0 +1,10 @@
+---
+"postgraphile": patch
+"ruru-components": patch
+"ruru": patch
+"grafserv": patch
+"grafast": patch
+---
+
+Add support for `onError` RFC with `PROPAGATE`, `NULL` and `HALT` behaviors
+implemented.