Use env files for secrets

Add env files back in for secrets - hides them from process lists and
allows you to pick up the latest env file when running
`kamal app exec` without reusing.

lib/kamal/commands/accessory.rb

@@ -1,7 +1,9 @@
 class Kamal::Commands::Accessory < Kamal::Commands::Base
   attr_reader :accessory_config
   delegate :service_name, :image, :hosts, :port, :files, :directories, :cmd,
-           :publish_args, :env_args, :volume_args, :label_args, :option_args, to: :accessory_config
+           :publish_args, :env_args, :volume_args, :label_args, :option_args,
+           :secrets_io, :secrets_path, :env_directory,
+           to: :accessory_config
 
   def initialize(config, name:)
     super(config)
@@ -98,6 +100,10 @@ class Kamal::Commands::Accessory < Kamal::Commands::Base
     docker :image, :rm, "--force", image
   end
 
+  def ensure_env_directory
+    make_directory env_directory
+  end
+
   private
     def service_filter
       [ "--filter", "label=service=#{service_name}" ]