Add kamal-proxy in experimental mode

The proxy can be enabled via the config:

```
proxy:
  enabled: true
  hosts:
    - 10.0.0.1
    - 10.0.0.2
```

This will enable the proxy and cause it to be run on the hosts listed
under `hosts`, after running `kamal proxy reboot`.

Enabling the proxy disables `kamal traefik` commands and replaces them
with `kamal proxy` ones. However only the marked hosts will run the
kamal-proxy container, the rest will run Traefik as before.

test/cli/proxy_test.rb

@@ -0,0 +1,141 @@
+require_relative "cli_test_case"
+
+class CliProxyTest < CliTestCase
+  test "boot" do
+    run_command("boot").tap do |output|
+      assert_match "docker login", output
+      assert_match "docker run --name kamal-proxy --detach --restart unless-stopped --publish 80:80 --publish 443:443 --volume /var/run/docker.sock:/var/run/docker.sock --volume kamal-proxy:/root/.config/kamal-proxy --log-opt max-size=\"10m\" #{Kamal::Configuration::Proxy::DEFAULT_IMAGE}", output
+    end
+  end
+
+  test "reboot" do
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-123$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{.NetworkSettings.IPAddress}}{{range $k, $v := .NetworkSettings.Ports}}{{printf \":%s\" $k}}{{break}}{{end}}'", "|", :sed, "-e", "'s/\\/tcp$//'")
+      .returns("172.1.0.2:80")
+      .at_least_once
+
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with { |*args| args[0..1] == [ :sh, "-c" ] }
+      .returns("123")
+      .at_least_once
+
+    run_command("reboot", "-y").tap do |output|
+      assert_match "docker container stop kamal-proxy on 1.1.1.1", output
+      assert_match "docker container stop traefik on 1.1.1.1", output
+      assert_match "docker container prune --force --filter label=org.opencontainers.image.title=kamal-proxy on 1.1.1.1", output
+      assert_match "docker container prune --force --filter label=org.opencontainers.image.title=Traefik on 1.1.1.1", output
+      assert_match "docker run --name kamal-proxy --detach --restart unless-stopped --publish 80:80 --publish 443:443 --volume /var/run/docker.sock:/var/run/docker.sock --volume kamal-proxy:/root/.config/kamal-proxy --log-opt max-size=\"10m\" #{Kamal::Configuration::Proxy::DEFAULT_IMAGE} on 1.1.1.1", output
+      assert_match "docker exec kamal-proxy kamal-proxy deploy app-web --target \"172.1.0.2:80\" --deploy-timeout \"6s\" on 1.1.1.1", output
+
+      assert_match "docker container stop kamal-proxy on 1.1.1.2", output
+      assert_match "docker container stop traefik on 1.1.1.2", output
+      assert_match "docker container prune --force --filter label=org.opencontainers.image.title=kamal-proxy on 1.1.1.2", output
+      assert_match "docker container prune --force --filter label=org.opencontainers.image.title=Traefik on 1.1.1.2", output
+      assert_match "docker run --name traefik --detach --restart unless-stopped --publish 80:80 --volume /var/run/docker.sock:/var/run/docker.sock --env-file .kamal/env/traefik/traefik.env --log-opt max-size=\"10m\" --label traefik.http.routers.catchall.entryPoints=\"http\" --label traefik.http.routers.catchall.rule=\"PathPrefix(\\`/\\`)\" --label traefik.http.routers.catchall.service=\"unavailable\" --label traefik.http.routers.catchall.priority=\"1\" --label traefik.http.services.unavailable.loadbalancer.server.port=\"0\" traefik:v2.10 --providers.docker --log.level=\"DEBUG\" on 1.1.1.2", output
+    end
+  end
+
+  test "reboot --rolling" do
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-123$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{.NetworkSettings.IPAddress}}{{range $k, $v := .NetworkSettings.Ports}}{{printf \":%s\" $k}}{{break}}{{end}}'", "|", :sed, "-e", "'s/\\/tcp$//'")
+      .returns("172.1.0.2:80")
+      .at_least_once
+
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with { |*args| args[0..1] == [ :sh, "-c" ] }
+      .returns("123")
+      .at_least_once
+
+    run_command("reboot", "--rolling", "-y").tap do |output|
+      assert_match "Running docker container prune --force --filter label=org.opencontainers.image.title=kamal-proxy on 1.1.1.1", output
+    end
+  end
+
+  test "start" do
+    run_command("start").tap do |output|
+      assert_match "docker container start kamal-proxy", output
+    end
+  end
+
+  test "stop" do
+    run_command("stop").tap do |output|
+      assert_match "docker container stop kamal-proxy", output
+    end
+  end
+
+  test "restart" do
+    Kamal::Cli::Proxy.any_instance.expects(:stop)
+    Kamal::Cli::Proxy.any_instance.expects(:start)
+
+    run_command("restart")
+  end
+
+  test "details" do
+    run_command("details").tap do |output|
+      assert_match "docker ps --filter name=^kamal-proxy$", output
+    end
+  end
+
+  test "logs" do
+    SSHKit::Backend::Abstract.any_instance.stubs(:capture)
+      .with(:docker, :logs, "kamal-proxy", " --tail 100", "--timestamps", "2>&1")
+      .returns("Log entry")
+
+    SSHKit::Backend::Abstract.any_instance.stubs(:capture)
+      .with(:docker, :logs, "traefik", " --tail 100", "--timestamps", "2>&1")
+      .returns("Log entry")
+
+    run_command("logs").tap do |output|
+      assert_match "Proxy Host: 1.1.1.1", output
+      assert_match "Log entry", output
+    end
+  end
+
+  test "logs with follow" do
+    SSHKit::Backend::Abstract.any_instance.stubs(:exec)
+      .with("ssh -t root@1.1.1.1 -p 22 'docker logs kamal-proxy --timestamps --tail 10 --follow 2>&1'")
+
+    assert_match "docker logs kamal-proxy --timestamps --tail 10 --follow", run_command("logs", "--follow")
+  end
+
+  test "remove" do
+    Kamal::Cli::Proxy.any_instance.expects(:stop)
+    Kamal::Cli::Proxy.any_instance.expects(:remove_container)
+    Kamal::Cli::Proxy.any_instance.expects(:remove_image)
+
+    run_command("remove")
+  end
+
+  test "remove_container" do
+    run_command("remove_container").tap do |output|
+      assert_match "docker container prune --force --filter label=org.opencontainers.image.title=kamal-proxy", output
+    end
+  end
+
+  test "remove_image" do
+    run_command("remove_image").tap do |output|
+      assert_match "docker image prune --all --force --filter label=org.opencontainers.image.title=kamal-proxy", output
+    end
+  end
+
+  test "commands disallowed when proxy is disabled" do
+    assert_raises_when_disabled "boot"
+    assert_raises_when_disabled "reboot"
+    assert_raises_when_disabled "start"
+    assert_raises_when_disabled "stop"
+    assert_raises_when_disabled "details"
+    assert_raises_when_disabled "logs"
+    assert_raises_when_disabled "remove"
+  end
+
+  private
+    def run_command(*command, fixture: :with_proxy)
+      stdouted { Kamal::Cli::Proxy.start([ *command, "-c", "test/fixtures/deploy_#{fixture}.yml" ]) }
+    end
+
+    def assert_raises_when_disabled(command)
+      assert_raises "kamal proxy commands are disabled unless experimental proxy support is enabled. Use `kamal traefik` commands instead." do
+        run_command(command, fixture: :with_accessories)
+      end
+    end
+end