Document environment abstraction

This commit replace the two empty "chapters" dedicated to profiles
and property source to an 'Environment abstraction' chapter that
covers both.

Issue: SPR-12107
Allow setting SockJsMessageCodec in WebSocket config

Issue: SPR-12091
Allow configuration of custom redirect patterns

This change enables the ability to configure
ViewNameMethodReturnValueHandler & ModelAndViewMethodReturnValueHandler
with patterns to use to test for a custom redirect view name.

Issue: SPR-12054