Spring Add runtime hints for WebFlux's WebSocket upgrade strategies

Tested using the webflux-netty smoke test and a local build of these changes: https://ge.spring.io/s/nvq4vhd5i2gh4.

Comment From: sdeleuze

Thanks for this PR, but I implemented that fix differently in #29146 in order to reuse the detection logic already implemented and only register the needed reflection entry.