cmd/k8s-operator,k8s-operator: Kubernetes Peer Relays (#20495)

This commit contains the Kubernetes implementation of peer relays via the new `PeerRelay` CRD. It's a mega branch consisting of the commits of other PRs gone into this work:

1. https://github.com/tailscale/tailscale/pull/20211
2. https://github.com/tailscale/tailscale/pull/20329
3. https://github.com/tailscale/tailscale/pull/20423
4. https://github.com/tailscale/tailscale/pull/20503

An instance of the `PeerRelay` CRD deploys a `StatefulSet` of containerboot instances configured to advertise themselves as peer relays using the IP addresses configured via `LoadBalancer` services on each cloud provider (with some AWS specifics as it's less automatic than its competing cloud providers). 

Per replica, a `LoadBalancer` type `Service` resource is provisioned and its IP address is used to configure the respective relay.

This has been tested with success in AWS, GCP & Azure and provides additional modification to `Service` resources via the CRD for any other kinds of deployment environments. It also contains some work that may appear to be duplication of what already exists within `cmd/k8s-operator` so we can start building an appropriate migration path for `Connector`, `ProxyGroup` etc into respective `k8s-operator/reconciler/*` packages.

Closes https://github.com/tailscale/corp/issues/34524

kube/kubetypes/types.go

@@ -34,6 +34,7 @@ const (
 	MetricProxyGroupIngressCount         = "k8s_proxygroup_ingress_resources"
 	MetricProxyGroupAPIServerCount       = "k8s_proxygroup_kube_apiserver_resources"
 	MetricTailnetCount                   = "k8s_tailnet_resources"
+	MetricPeerRelayCount                 = "k8s_peerrelay_resources"
 
 	// Keys that containerboot writes to state file that can be used to determine its state.
 	// fields set in Tailscale state Secret. These are mostly used by the Tailscale Kubernetes operator to determine