Spring SPR-15030: Allow to specify serialization hints to the functional web server

Could you review this in order to allow me to push in master @poutsma?

Comment From: poutsma

As I said on Slack: this looks good to me. The only two additions I would like to see before we merge are: javadoc, and a similar hints mechanism for the BodyExtractor

Comment From: sdeleuze

Merged via fbf88d19da1a9a80c8f0e4d5854723a451910cf1.