Fix our install doc on gw API

[linsun]

Ran into this today while following the doc:

 ~/Downloads/ kubectl get crd gateways.gateway.networking.k8s.io &> /dev/null ||
{ kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.2.0/standard-install.yaml\; }

error: unable to read URL "https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.2.0/standard-install.yaml;", server reported 404 Not Found, status code=404

Fixed by this:

 ~/Downloads/ kubectl get crd gateways.gateway.networking.k8s.io &> /dev/null ||
{ kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.2.0/standard-install.yaml }

customresourcedefinition.apiextensions.k8s.io/gatewayclasses.gateway.networking.k8s.io created
customresourcedefinition.apiextensions.k8s.io/gateways.gateway.networking.k8s.io created
customresourcedefinition.apiextensions.k8s.io/grpcroutes.gateway.networking.k8s.io created
customresourcedefinition.apiextensions.k8s.io/httproutes.gateway.networking.k8s.io created
customresourcedefinition.apiextensions.k8s.io/referencegrants.gateway.networking.k8s.io created