added Containerfile.splitter

Containerfile.splitter

@@ -0,0 +1,16 @@
+# This file is used to split existing images using `buildah build`. See
+# README.md for how to use it.
+
+ARG CHUNKAH=quay.io/coreos/chunkah:latest@sha256:352097f3d32186ac11082f8b74cd544678b00388b50c96ba5c8e79503a454fe3
+ARG CHUNKAH_ARGS=""
+ARG CHUNKAH_CONFIG_STR
+
+FROM overridden AS target
+FROM ${CHUNKAH} AS chunkah
+ARG CHUNKAH_CONFIG_STR
+ARG CHUNKAH_ARGS
+RUN --mount=type=bind,target=/run/src,rw \
+    --mount=from=target,target=/chunkah,ro \
+      chunkah build ${CHUNKAH_ARGS} --output oci:/run/src/out
+
+FROM oci:out