docs/envoy-authorization: update to transport APIv3, Envoy 1.17
docs/envoy-authorization: update to transport APIv3, Envoy 1.17

Recent versions of envoy's docker container have changed the way
dropping privileges works:

- it happens by default
- it's not driven by `securityContext.runAsUser`

So in the docker container's entrypoint, the environment will be
set up: /dev/std{err,out} will be chowned to an unprivileged user,
which will have uid ENVOY_UID. Hence we set that env variable to
match the UID we us with iptables in open-policy-agent/proxy_init.

Signed-off-by: Stephan Renatus <0d0a21c7604d0d452d5c1019ca18e48a97a9a057@gmail.com>

open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,tsandall/opa,tsandall/opa,open-policy-agent/opa,tsandall/opa,tsandall/opa,open-policy-agent/opa,open-policy-agent/opa,tsandall/opa,open-policy-agent/opa