cluster/admitomatic: finish up service

This turns admitomatic into a self-standing service that can be used as
an admission controller.

I've tested this E2E on a local k3s server, and have some early test
code for that - but that'll land up in a follow up CR, as it first needs
to be cleaned up.

Change-Id: I46da0fc49f9d1a3a1a96700a36deb82e5057249b
diff --git a/cluster/admitomatic/config/sample.pb.text b/cluster/admitomatic/config/sample.pb.text
new file mode 100644
index 0000000..21e98bc
--- /dev/null
+++ b/cluster/admitomatic/config/sample.pb.text
@@ -0,0 +1,7 @@
+allow_domain { namespace: "example" dns: "*.example.com" }
+allow_domain {
+  namespace: "personal-q3k" dns: "foo.q3k.org"
+}
+allow_domain {
+  namespace: "personal-q3k" dns: "bar.q3k.org"
+}