FR: generate Gateway+ServiceEntry from k8s ingress resource

[ZackButcher]

There used to be a tool in istioctl to do this (that was removed before 1.0), I think it'd be worth resurrecting here as it's still a common stumbling block for people moving from k8s. We can definitely cover transforming a basic ingress into a Gateway+VS easily, which covers the 80% use case. There's likely a subset of annotations that it would be worthwhile to handle as well.

[mt-inside]

a) never knew that existed
b) very useful, wtf was it deleted?
c) thanks