Add extension to set/delete cookies

[waiting-for-dev]

This extension helps with the addition of the Set-Cookie header
to the response, which is the way the server has to instruct the
browser to keep a cookie. A cookie can be added with the
#add_cookie method, while it can be marked for deletion with
#delete_cookie. Remember that marking a cookie for deletion just
means adding the same cookie name with an expiration time in the
past.

require 'web_pipe'

WebPipe.load_extensions(:cookies)

class SetCookie
  include WebPipe

  plug :set_cookie, ->(conn) { conn.set_cookie('foo', 'bar', path: '/') }
end

class DeleteCookie
  include WebPipe

  plug :delete_cookie, ->(conn) { conn.delete_cookie('foo', path: '/') }
end