Accessories aren't required to publish a port

Allows for background accessories like schedulers that don't act
as typical network service dependencies and have no port to expose.

lib/mrsk/commands/accessory.rb

@@ -1,6 +1,6 @@
 class Mrsk::Commands::Accessory < Mrsk::Commands::Base
   attr_reader :accessory_config
-  delegate :service_name, :image, :host, :port, :files, :directories, :env_args, :volume_args, :label_args, to: :accessory_config
+  delegate :service_name, :image, :host, :port, :files, :directories, :publish_args, :env_args, :volume_args, :label_args, to: :accessory_config
 
   def initialize(config, name:)
     super(config)
@@ -13,7 +13,7 @@ class Mrsk::Commands::Accessory < Mrsk::Commands::Base
       "--detach",
       "--restart", "unless-stopped",
       "--log-opt", "max-size=#{MAX_LOG_SIZE}",
-      "--publish", port,
+      *publish_args,
       *env_args,
       *volume_args,
       *label_args,

lib/mrsk/configuration/accessory.rb

@@ -20,13 +20,15 @@ class Mrsk::Configuration::Accessory
   end
 
   def port
-    if specifics["port"].to_s.include?(":")
-      specifics["port"]
-    else
-      "#{specifics["port"]}:#{specifics["port"]}"
+    if port = specifics["port"]&.to_s
+      port.include?(":") ? port : "#{port}:#{port}"
     end
   end
 
+  def publish_args
+    argumentize "--publish", port if port
+  end
+
   def labels
     default_labels.merge(specifics["labels"] || {})
   end