`stunnerctl config` does not fall back to the default namespace

[rg0now]

Description

If no namespace is given, stunnerctl config should automatically use the default namespace.

Steps to Reproduce

1. Deploy the UDP greeter example into the default namesapce:

   apiVersion: gateway.networking.k8s.io/v1
   kind: GatewayClass
   metadata:
    name: stunner-gatewayclass
   spec:
    controllerName: "stunner.l7mp.io/gateway-operator"
    parametersRef:
      group: "stunner.l7mp.io"
      kind: GatewayConfig
      name: stunner-gatewayconfig
      namespace: default
    description: "STUNner is a WebRTC ingress gateway for Kubernetes"
   ---
   
   apiVersion: stunner.l7mp.io/v1
   kind: GatewayConfig
   metadata:
    name: stunner-gatewayconfig
   spec:
    realm: stunner.l7mp.io
    authType: plaintext
    userName: "user-1"
    password: "pass-1"
   
   ---
   apiVersion: gateway.networking.k8s.io/v1
   kind: Gateway
   metadata:
    name: udp-gateway
   spec:
    gatewayClassName: stunner-gatewayclass
    listeners:
      - name: udp-listener
        port: 3478
        protocol: TURN-UDP
   ---
   apiVersion: gateway.networking.k8s.io/v1
   kind: Gateway
   metadata:
    name: tcp-gateway
   spec:
    gatewayClassName: stunner-gatewayclass
    listeners:
      - name: tcp-listener
        port: 3478
        protocol: TURN-TCP
   ---
   apiVersion: stunner.l7mp.io/v1
   kind: UDPRoute
   metadata:
    name: media-plane
   spec:
    parentRefs:
      - name: udp-gateway
      - name: tcp-gateway
    rules:
      - backendRefs:
          - name: media-plane

2. Query the dataplane config with stunnerctl but do not specify the namespace:

   stunnerctl config udp-gateway

Expected behavior: stunnerctl should use the default namespace.

Actual behavior: It leaves the namespace unspecified and fails to find the gateway. Using an explicit namespace works though:

stunnerctl -n default config udp-gateway 
Gateway: default/udp-gateway (loglevel: "all:INFO")
Authentication type: static, username/password: user-1/pass-1
Listeners:
...

Versions

Regression appeared during the stunnerctl rewrite.