cmd/{containerboot,k8s-operator}: reissue auth keys for broken proxies (#16450)

Adds logic for containerboot to signal that it can't auth, so the
operator can reissue a new auth key. This only applies when running with
a config file and with a kube state store.

If the operator sees reissue_authkey in a state Secret, it will create a
new auth key iff the config has no auth key or its auth key matches the
value of reissue_authkey from the state Secret. This is to ensure we
don't reissue auth keys in a tight loop if the proxy is slow to start or
failing for some other reason. The reissue logic also uses a burstable
rate limiter to ensure there's no way a terminally misconfigured
or buggy operator can automatically generate new auth keys in a tight loop.

Additional implementation details (ChaosInTheCRD):

- Added `ipn.NotifyInitialHealthState` to ipn watcher, to ensure that
  `n.Health` is populated when notify's are returned.
- on auth failure, containerboot:
  - Disconnects from control server
  - Sets reissue_authkey marker in state Secret with the failing key
  - Polls config file for new auth key (10 minute timeout)
  - Restarts after receiving new key to apply it

- modified operator's reissue logic slightly:
  - Deletes old device from tailnet before creating new key
  - Rate limiting: 1 key per 30s with initial burst equal to replica count
  - In-flight tracking (authKeyReissuing map) prevents duplicate API calls
    across reconcile loops

Updates #14080

Change-Id: I6982f8e741932a6891f2f48a2936f7f6a455317f


(cherry picked from commit 969927c47c3d4de05e90f5b26a6d8d931c5ceed4)

Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>
Co-authored-by: chaosinthecrd <tom@tmlabs.co.uk>

cmd/k8s-operator/operator.go

@@ -20,6 +20,7 @@ import (
 	"github.com/go-logr/zapr"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
+	"golang.org/x/time/rate"
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	discoveryv1 "k8s.io/api/discovery/v1"
@@ -723,6 +724,8 @@ func runReconcilers(opts reconcilerOpts) {
 			tsFirewallMode:    opts.proxyFirewallMode,
 			defaultProxyClass: opts.defaultProxyClass,
 			loginServer:       opts.tsServer.ControlURL,
+			authKeyRateLimits: make(map[string]*rate.Limiter),
+			authKeyReissuing:  make(map[string]bool),
 		})
 	if err != nil {
 		startlog.Fatalf("could not create ProxyGroup reconciler: %v", err)