This commit introduces JSON streaming support which consists of serializing HTTP request with application/stream+json media type as line delimited JSON.

It also optimize Flux serialization for application/json by using flux.collectList() and a single Jackson invocation instead of one call per element previous strategy. This change result in a x4 throughput improvement for collection with a lot of small elements.

Issues: SPR-15095, SPR-15104

Comment From: sdeleuze

Merged with https://github.com/spring-projects/spring-framework/commit/6b9b0230c4de394348c42b6f5964fc66eb659dd3