cmd/k8s-operator: add metrics to track usage

Updates #502

Signed-off-by: Maisem Ali <maisem@tailscale.com>

cmd/k8s-operator/proxy.go

@@ -25,6 +25,7 @@ import (
 	"tailscale.com/tailcfg"
 	"tailscale.com/tsnet"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/set"
 )
 
@@ -42,6 +43,8 @@ func addWhoIsToRequest(r *http.Request, who *apitype.WhoIsResponse) *http.Reques
 	return r.WithContext(context.WithValue(r.Context(), whoIsKey{}, who))
 }
 
+var counterNumRequestsProxied = clientmetric.NewCounter("k8s_auth_proxy_requests_proxied")
+
 // launchAuthProxy launches the auth proxy, which is a small HTTP server that
 // authenticates requests using the Tailscale LocalAPI and then proxies them to
 // the kube-apiserver.
@@ -84,6 +87,7 @@ func (h *authProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "failed to authenticate caller", http.StatusInternalServerError)
 		return
 	}
+	counterNumRequestsProxied.Add(1)
 	h.rp.ServeHTTP(w, addWhoIsToRequest(r, who))
 }