Revise GEP-1713: Update gateway status and conformance test details for ListenerSets

apis/v1/gateway_types.go

@@ -998,6 +998,24 @@ type GatewayStatus struct {
 	// +listMapKey=name
 	// +kubebuilder:validation:MaxItems=64
 	Listeners []ListenerStatus `json:"listeners,omitempty"`
+
+	// AttachedListeners represents the total number of ListenerSets that have been
+	// successfully attached to this Gateway.
+	//
+	// Successful attachment of a ListenerSets to a Gateway is based solely on the
+	// combination of the AllowedListeners field on the Gateway
+	// and the ListenerSets's ParentRefs field. A ListenerSets is successfully attached to
+	// a Gateway when it is selected by the ListenerSets's AllowedListeners field
+	// AND the ListenerSets has a valid ParentRef selecting the Gateway
+	// resource as a parent resource. ListenerSets status does not impact
+	// successful attachment, i.e. the AttachedListeners field count MUST be set
+	// for ListenerSets with condition Accepted: false and MUST count successfully
+	// attached AttachedListeners that may themselves have Accepted: false conditions.
+	//
+	// Uses for this field include troubleshooting AttachedListeners attachment and
+	// measuring blast radius/impact of changes to a Gateway.
+	// +optional
+	AttachedListeners int32 `json:"attachedListeners"`
 }
 
 // GatewayInfrastructure defines infrastructure level attributes about a Gateway instance.