envknob,kube/kubetypes,cmd/k8s-operator: add app type for ProxyGroup (#14029)

Sets a custom hostinfo app type for ProxyGroup replicas, similarly
to how we do it for all other Kubernetes Operator managed components.

Updates tailscale/tailscale#13406,tailscale/corp#22920

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

cmd/k8s-operator/proxygroup_specs.go

@@ -15,6 +15,7 @@ import (
 	"sigs.k8s.io/yaml"
 	tsapi "tailscale.com/k8s-operator/apis/v1alpha1"
 	"tailscale.com/kube/egressservices"
+	"tailscale.com/kube/kubetypes"
 	"tailscale.com/types/ptr"
 )
 
@@ -146,6 +147,10 @@ func pgStatefulSet(pg *tsapi.ProxyGroup, namespace, image, tsFirewallMode, cfgHa
 				Name:  "TS_USERSPACE",
 				Value: "false",
 			},
+			{
+				Name:  "TS_INTERNAL_APP",
+				Value: kubetypes.AppProxyGroupEgress,
+			},
 		}
 
 		if tsFirewallMode != "" {