Find a reasonable way to enable conditional replacement

[stepro]

Something like this:

kdo -c svc/backend-api -R --when '80.http.header.Foo eq bar' -it .

This would inherit the config of the backend-api service but instead of unconditionally redirecting to the kdo pod, it would only redirect when an incoming http request on port 80 has the header "Foo" equal to "bar". The when flag would need to have some relatively expressive language to allow for a variety of conditions.