metropolis/build: add kube-code-generator

This implements kube-code-generator, a set of Bazel rules for generating
Kubernetes resource APIs based on a Go library, using
k8s.io/code-generator.

Test Plan: Was considering adding a test for this - but this is practically best tested with the next change in the stack, which actually uses it to implement the VM hypervisor kube API.

X-Origin-Diff: phab/D751
GitOrigin-RevId: 31e3b632c2e83282c8b2c415402cddea66d4ce51
diff --git a/metropolis/build/kube-code-generator/boilerplate.go.txt b/metropolis/build/kube-code-generator/boilerplate.go.txt
new file mode 100644
index 0000000..ef05f6f
--- /dev/null
+++ b/metropolis/build/kube-code-generator/boilerplate.go.txt
@@ -0,0 +1 @@
+// Code generated by //metropolis/build/kubernetes-code-generator. Do not commit to source control.