All role specific proxy configuration

By default only the primary role runs the proxy. To disable the proxy
for that role, you can set `proxy: false` under it.

For other roles they default to not running the proxy, but you can
enable it by setting `proxy: true` for the role, or alternatively
setting a proxy configuration.

The proxy configuration will be merged into the root proxy configuration.

test/configuration/role_test.rb

@@ -250,6 +250,14 @@ class ConfigurationRoleTest < ActiveSupport::TestCase
     assert_equal [ "-t", 30 ], config_with_roles.role(:workers).stop_args
   end
 
+  test "role specific proxy config" do
+    @deploy_with_roles[:proxy] = { "response_timeout" => 15 }
+    @deploy_with_roles[:servers]["workers"]["proxy"] = { "response_timeout" => 18 }
+
+    assert_equal "15s", config_with_roles.role(:web).proxy.deploy_options[:"target-timeout"]
+    assert_equal "18s", config_with_roles.role(:workers).proxy.deploy_options[:"target-timeout"]
+  end
+
   private
     def config
       Kamal::Configuration.new(@deploy)