Deprecate gateway_api_experimental_channel

Please use `gateway_api_channel` and set `experimental`.

Signed-off-by: ChengHao Yang <[email protected]>

Author: tico88612

inventory/sample/group_vars/k8s_cluster/addons.yml

@@ -67,7 +67,6 @@ local_volume_provisioner_enabled: false
 
 # Gateway API CRDs
 gateway_api_enabled: false
-# gateway_api_experimental_channel: false
 
 # Nginx ingress controller deployment
 ingress_nginx_enabled: false