Add autoloads for lib/gitlab/satellite/files/*

These files don't match their naming convention, but for organizational
purposes it makes sense.

lib/gitlab/satellite/satellite.rb

 module Gitlab
   module Satellite
+    autoload :DeleteFileAction, 'gitlab/satellite/files/delete_file_action'
+    autoload :EditFileAction,   'gitlab/satellite/files/edit_file_action'
+    autoload :FileAction,       'gitlab/satellite/files/file_action'
+    autoload :NewFileAction,    'gitlab/satellite/files/new_file_action'
+
     class CheckoutFailed < StandardError; end
     class CommitFailed < StandardError; end
     class PushFailed < StandardError; end