Allow setting internal redirect policy in BackendTrafficPolicy

Description:

My team is now working on migrating from ingress-nginx to envoy gateway. One of our use case for ingress-nginx is to redirect to some s3 endpoint based on the response header X-Accel-Redirect returned from backend service.

envoy proxy seems to have similar functionality called internal_redirect_policy, but it's hard to use with envoy gateway.

it would be very helpful if it is integrated in BackendTrafficPolicy.