builder: New container image

This will be the container image buildroot.

TODO: Build this using RHTAP too

builder/Containerfile

@@ -0,0 +1,5 @@
+# This image contains the baseline tools to build bootable base images.
+FROM quay.io/centos/centos:stream9
+COPY coreos-continuous.repo /etc/yum.repos.d
+COPY . /src
+RUN /src/build.sh && cd / && rm /src -rf