nodes/4.2/4.2.0-rc.4: Add a new release

Luke pushed this up to Quay on the 10th.  Generated with:

  $ hack/graph-util.py update-node quay.io/openshift-release-dev/ocp-release:4.2.0-rc.4

But that hit [1], so we're not going to tag it into 4.2.z.

[1]: https://bugzilla.redhat.com/show_bug.cgi?id=1721583

nodes/4.2/4.2.0-rc.4.json

@@ -0,0 +1,7 @@
+{
+  "metadata": {
+    "url": "https://access.redhat.com/errata/RHBA-2019:2922"
+  },
+  "payload": "quay.io/openshift-release-dev/ocp-release@sha256:2ed0897c27fe0f2e27591da81f1f73c8cfefec6dfd4d3e67a68481d0efe38148",
+  "version": "4.2.0-rc.4"
+}