Use Volume for kamal proxy config volume

lib/kamal/commands/proxy.rb

@@ -17,7 +17,7 @@ class Kamal::Commands::Proxy < Kamal::Commands::Base
       "--restart", "unless-stopped",
       *proxy_config.publish_args,
       "--volume", "/var/run/docker.sock:/var/run/docker.sock",
-      "--volume", "#{proxy_config.config_directory_as_docker_volume}:/root/.config/kamal-proxy",
+      *proxy_config.config_volume.docker_args,
       *config.logging_args,
       proxy_config.image
   end

lib/kamal/configuration.rb

@@ -207,10 +207,6 @@ class Kamal::Configuration
   end
 
 
-  def run_directory_as_docker_volume
-    File.join "$(pwd)", run_directory
-  end
-
   def hooks_path
     raw_config.hooks_path || ".kamal/hooks"
   end

lib/kamal/configuration/proxy.rb

@@ -59,8 +59,10 @@ class Kamal::Configuration::Proxy
     optionize deploy_options
   end
 
-  def config_directory_as_docker_volume
+  def config_volume
-    File.join config.run_directory_as_docker_volume, "proxy", "config"
+    Kamal::Configuration::Volume.new \
+      host_path: File.join(config.run_directory, "proxy", "config"),
+      container_path: "/root/.config/kamal-proxy"
   end
 
   private

test/configuration_test.rb

@@ -291,11 +291,6 @@ class ConfigurationTest < ActiveSupport::TestCase
     assert_equal ".kamal", config.run_directory
   end
 
-  test "run directory as docker volume" do
-    config = Kamal::Configuration.new(@deploy)
-    assert_equal "$(pwd)/.kamal", config.run_directory_as_docker_volume
-  end
-
   test "asset path" do
     assert_nil @config.asset_path
     assert_equal "foo", Kamal::Configuration.new(@deploy.merge!(asset_path: "foo")).asset_path