Enable garden DNS proxy in docker-compose

The `CONCOURSE_GARDEN_DNS_PROXY_ENABLE` flag was taken out of the dev
image in db8c43e565
In order for local docker-compose DNS to work with latest concourse/dev
image we need to renable it. Since Guardian is still the default in
docker-compose.yml it makes sense to use it there and unset it in the
containerd override.

Signed-off-by: Andy Paine <andy.paine@engineerbetter.com>

docker-compose.yml

@@ -52,3 +52,4 @@ services:
       # so we can reach Garden/Baggageclaim for debugging
       CONCOURSE_BIND_IP: 0.0.0.0
       CONCOURSE_BAGGAGECLAIM_BIND_IP: 0.0.0.0
+      CONCOURSE_GARDEN_DNS_PROXY_ENABLE: "true"

hack/overrides/containerd.yml

@@ -9,3 +9,5 @@ services:
   worker:
     environment:
       CONCOURSE_RUNTIME: containerd
+      CONCOURSE_GARDEN_DNS_PROXY_ENABLE: ~
+      CONCOURSE_CONTAINERD_DNS_PROXY_ENABLE: "true"