Add a writable proxy volume

Maps in and external /home/kamal-proxy/.app-config volume that we can
use to map files to the proxy.

Can be used to store custom maintenance pages or SSL certificates.

lib/kamal/commands/proxy.rb

@@ -109,6 +109,7 @@ class Kamal::Commands::Proxy < Kamal::Commands::Base
         "--network", "kamal",
         "--detach",
         "--restart", "unless-stopped",
-        "--volume", "kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy"
+        "--volume", "kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy",
+        *config.proxy_app_config_volume.docker_args
     end
 end

lib/kamal/configuration.rb

@@ -300,6 +300,16 @@ class Kamal::Configuration
     File.join proxy_directory, "image_version"
   end
 
+  def proxy_app_config_directory
+    File.join proxy_directory, "app-config"
+  end
+
+  def proxy_app_config_volume
+    Volume.new \
+      host_path: proxy_app_config_directory,
+      container_path: "/home/kamal-proxy/.app-config"
+  end
+
   def to_h
     {
       roles: role_names,

test/cli/proxy_test.rb

@@ -56,12 +56,12 @@ class CliProxyTest < CliTestCase
     run_command("reboot", "-y").tap do |output|
       assert_match "docker container stop kamal-proxy 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 "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy on 1.1.1.1", output
+      assert_match "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy --volume $(pwd)/.kamal/proxy/app-config:/home/kamal-proxy/.app-config on 1.1.1.1", output
       assert_match "docker exec kamal-proxy kamal-proxy deploy app-web --target=\"abcdefabcdef:80\" --deploy-timeout=\"6s\" --drain-timeout=\"30s\" --buffer-requests --buffer-responses --log-request-header=\"Cache-Control\" --log-request-header=\"Last-Modified\" --log-request-header=\"User-Agent\" on 1.1.1.1", output
 
       assert_match "docker container stop kamal-proxy 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 "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy on 1.1.1.2", output
+      assert_match "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy --volume $(pwd)/.kamal/proxy/app-config:/home/kamal-proxy/.app-config on 1.1.1.2", output
       assert_match "docker exec kamal-proxy kamal-proxy deploy app-web --target=\"abcdefabcdef:80\" --deploy-timeout=\"6s\" --drain-timeout=\"30s\" --buffer-requests --buffer-responses --log-request-header=\"Cache-Control\" --log-request-header=\"Last-Modified\" --log-request-header=\"User-Agent\" on 1.1.1.2", output
     end
   end

test/commands/proxy_test.rb

@@ -15,7 +15,7 @@ class CommandsProxyTest < ActiveSupport::TestCase
 
   test "run" do
     assert_equal \
-      "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy",
+      "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy --volume $(pwd)/.kamal/proxy/app-config:/home/kamal-proxy/.app-config",
       new_command.run.join(" ")
   end
 
@@ -23,7 +23,7 @@ class CommandsProxyTest < ActiveSupport::TestCase
     @config.delete(:proxy)
 
     assert_equal \
-      "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy",
+      "echo $(cat .kamal/proxy/options 2> /dev/null || echo \"--publish 80:80 --publish 443:443 --log-opt max-size=10m\") $(cat .kamal/proxy/image 2> /dev/null || echo \"basecamp/kamal-proxy\"):$(cat .kamal/proxy/image_version 2> /dev/null || echo \"#{Kamal::Configuration::PROXY_MINIMUM_VERSION}\") | xargs docker run --name kamal-proxy --network kamal --detach --restart unless-stopped --volume kamal-proxy-config:/home/kamal-proxy/.config/kamal-proxy --volume $(pwd)/.kamal/proxy/app-config:/home/kamal-proxy/.app-config",
       new_command.run.join(" ")
   end