Add ability to extend rails server command options parser

[a-chernykh]

With this change it will be possible to add additional options to the option_parser like this:

require 'rails/commands/server'
module Rails
  class Server < ::Rack::Server
    class Options
      def option_parser_with_open(options)
        parser = option_parser_without_open options
        parser.on('-o', '--open', 'Open in default browser') { options[:open] = true }
        parser
      end
      alias_method_chain :option_parser, :open
    end

    def start_with_open
      start_without_open do
        `open http://localhost:3000` if options[:open]
      end
    end
    alias_method_chain :start, :open
  end
end

[a-chernykh]

I really like to see rails server -o feature merged which opens server in a browser. Since #9396 have not received much traction I've decided to create a gem which adds this option, but I need OptionParser to be extendable first.