Add sig-network-ingress2gateway channel to YAML

Author: Stevenjin8

communication/slack-config/channels.yaml

@@ -507,6 +507,7 @@ channels:
   - name: sig-multicluster
   - name: sig-network
   - name: sig-network-agentic-networking
+  - name: sig-network-ingress2gateway
   - name: sig-network-kni
   - name: sig-network-multi-network
   # sig-node channels are defined in sig-node/