feat: Docker test image

Simple Docker image to manually test the build-and-push Github Action

Author: jjmaestro

buildkite/docker/testimage/Dockerfile

@@ -0,0 +1,11 @@
+FROM busybox:stable AS testimage-base
+RUN mkdir /tmp/base
+
+FROM testimage-base AS testimage-target1
+RUN mkdir /tmp/base/target1
+
+FROM testimage-base AS testimage-target2-nojdk
+RUN mkdir /tmp/base/target2
+
+FROM testimage-target2-nojdk AS testimage-target3
+RUN mkdir /tmp/base/target3