Add Wireguard-based K8s pod networking

This adds a pod networking runnable based on Wireguard which watches all nodes
and adds their K8s IPAM allocations as routes into the kernel & WireGuard. It only depends
on K8s and only performs direct routing.

Test Plan: Manually tested by spinning up a two-node cluster and running two Alpine pods pinging eachother. Can be covered by E2E tests once we can do image preseeding for the test infra (T793).

Bug: T487

X-Origin-Diff: phab/D573
GitOrigin-RevId: ba3fc36f421fd75002f6cf8bea25ed6f1eb457b0
diff --git a/core/internal/kubernetes/controller-manager.go b/core/internal/kubernetes/controller-manager.go
index 0934ae1..8a85a99 100644
--- a/core/internal/kubernetes/controller-manager.go
+++ b/core/internal/kubernetes/controller-manager.go
@@ -41,6 +41,8 @@
 	serverKey             []byte
 }
 
+var clusterNet = net.IPNet{IP: net.IP{10, 0, 0, 0}, Mask: net.IPMask{255, 255, 0, 0}}
+
 func getPKIControllerManagerConfig(ctx context.Context, kv clientv3.KV, kpki *pki.KubernetesPKI) (*controllerManagerConfig, error) {
 	var config controllerManagerConfig
 	var err error
@@ -84,7 +86,10 @@
 				pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: config.serverCert})),
 			args.FileOpt("--tls-private-key-file", "server-key.pem",
 				pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: config.serverKey})),
+			"--allocate-node-cidrs",
+			"--cluster-cidr="+clusterNet.String(),
 		)
+
 		if args.Error() != nil {
 			return fmt.Errorf("failed to use fileargs: %w", err)
 		}