Configurable Kamal directory

To avoid polluting the default SSH directory with lots of Kamal config,
we'll default to putting them in a `kamal` sub directory.

But also make the directory configurable with the `run_directory` key,
so for example you can set it as `/var/run/kamal/`

The directory is created during bootstrap or before any command that
will need to access a file.

lib/kamal/commands/auditor.rb

@@ -19,7 +19,9 @@ class Kamal::Commands::Auditor < Kamal::Commands::Base
 
   private
     def audit_log_file
-      [ "kamal", config.service, config.destination, "audit.log" ].compact.join("-")
+      file = [ config.service, config.destination, "audit.log" ].compact.join("-")
+
+      "#{config.run_directory}/#{file}"
     end
 
     def audit_tags(**details)

lib/kamal/commands/lock.rb

@@ -40,7 +40,7 @@ class Kamal::Commands::Lock < Kamal::Commands::Base
     end
 
     def lock_dir
-      "kamal_lock-#{config.service}"
+      "#{config.run_directory}/lock-#{config.service}"
     end
 
     def lock_details_file

lib/kamal/commands/server.rb

@@ -0,0 +1,5 @@
+class Kamal::Commands::Server < Kamal::Commands::Base
+  def ensure_run_directory
+    [:mkdir, "-p", config.run_directory]
+  end
+end