cmd/{containerboot,k8s-operator}: use state Secret for checking device auth (#16328)

Previously, the operator checked the ProxyGroup status fields for
information on how many of the proxies had successfully authed. Use
their state Secrets instead as a more reliable source of truth.

containerboot has written device_fqdn and device_ips keys to the
state Secret since inception, and pod_uid since 1.78.0, so there's
no need to use the API for that data. Read it from the state Secret
for consistency. However, to ensure we don't read data from a
previous run of containerboot, make sure we reset containerboot's
state keys on startup.

One other knock-on effect of that is ProxyGroups can briefly be
marked not Ready while a Pod is restarting. Introduce a new
ProxyGroupAvailable condition to more accurately reflect
when downstream controllers can implement flows that rely on a
ProxyGroup having at least 1 proxy Pod running.

Fixes #16327

Change-Id: I026c18e9d23e87109a471a87b8e4fb6271716a66

Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>

cmd/k8s-operator/egress-services-readiness_test.go

@@ -137,7 +137,7 @@ func setReady(svc *corev1.Service, cl tstime.Clock, l *zap.SugaredLogger, replic
 }
 
 func setPGReady(pg *tsapi.ProxyGroup, cl tstime.Clock, l *zap.SugaredLogger) {
-	tsoperator.SetProxyGroupCondition(pg, tsapi.ProxyGroupReady, metav1.ConditionTrue, "foo", "foo", pg.Generation, cl, l)
+	tsoperator.SetProxyGroupCondition(pg, tsapi.ProxyGroupAvailable, metav1.ConditionTrue, "foo", "foo", pg.Generation, cl, l)
 }
 
 func setEndpointForReplica(pg *tsapi.ProxyGroup, ordinal int32, eps *discoveryv1.EndpointSlice) {