Add two new exchange attributes for request cookie and response cookie

CookieAttribute (%{c,cookie_name}) already exists for cookie. However, CookieAttribute#readAttribute() reads a request cookie and CookieAttribute#writeAttribute() writes a response cookie. This should have been two attributes, one for request cookie and another for response cookie.

The current CookieAttribute can't be changed due to compatibility concerns. So, we need to add two new attributes to fix this. I would like to propose the following two attributes:

• RequestCookieAttribute (%{req-cookie,cookie_name}) for request cookie
• ResponseCookieAttribute (%{resp-cookie,cookie_name}) for response cookie

If you have any other suggestion for the prefix name, please let me know.