OAuth2AuthorizeRequest supports attributes

[jgrandja]

We should add a member to OAuth2AuthorizeRequest of type Map<String, Object> that can be used for request attributes.

In addition to this change, we should remove the HttpServletRequest and HttpServletResponse members from OAuth2AuthorizeRequest and instead populate these into the request attributes member.

This will also allow us to reuse OAuth2AuthorizeRequest as input to ServerOAuth2AuthorizedClientManager.authorize() and remove ServerOAuth2AuthorizeRequest.