Custom proxy image registry, repo and version

Use the --registry, --repository and --image_version options of
`kamal proxy boot_config set` to change the kamal-proxy image used.

We'll still insist that the image version is at least as high as the
minimum.

test/integration/docker/deployer/app/.kamal/hooks/pre-deploy

@@ -1,3 +1,6 @@
 #!/bin/sh
+set -e
+
+kamal proxy boot_config set --registry registry:4443
 echo "Deployed!"
 mkdir -p /tmp/${TEST_ID} && touch /tmp/${TEST_ID}/pre-deploy

test/integration/docker/deployer/app_with_proxied_accessory/config/deploy.yml

@@ -41,4 +41,4 @@ accessories:
         interval: 1
         timeout: 1
         path: "/"
-
+drain_timeout: 2

test/integration/docker/deployer/app_with_roles/.kamal/hooks/pre-deploy

@@ -1,3 +1,6 @@
 #!/bin/sh
+set -e
+
+kamal proxy boot_config set --registry registry:4443
 echo "Deployed!"
 mkdir -p /tmp/${TEST_ID} && touch /tmp/${TEST_ID}/pre-deploy

test/integration/docker/deployer/app_with_traefik/.kamal/hooks/pre-deploy

@@ -1,4 +1,7 @@
-kamal proxy boot_config set --publish false \
+set -e
+
+kamal proxy boot_config set --registry registry:4443 \
+                            --publish false \
                             --docker_options label=traefik.http.services.kamal_proxy.loadbalancer.server.scheme=http \
                                              label=traefik.http.routers.kamal_proxy.rule=PathPrefix\(\`/\`\) \
                                              sysctl=net.ipv4.ip_local_port_range=\"10000\ 60999\"

test/integration/docker/deployer/setup.sh

@@ -20,6 +20,7 @@ push_image_to_registry_4443() {
 install_kamal
 push_image_to_registry_4443 nginx 1-alpine-slim
 push_image_to_registry_4443 busybox 1.36.0
+push_image_to_registry_4443 basecamp/kamal-proxy v0.8.7
 
 # .ssh is on a shared volume that persists between runs. Clean it up as the
 # churn of temporary vm IPs can eventually create conflicts.