Support server.compression for reactive servers

[unlimitedsola]

According to https://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#how-to-enable-http-response-compression
webflux with netty server currently doesn't support compression.

[snicoll]

@bclozel given that it's blocked and not scheduled for reactor-netty 0.8.0, I think this one should be postponed.

[bclozel]

@snicoll reactor-netty supports server compression with only one option: the minimum response size (see HttpServerOptions). We can provide that support.

To be on par with the other servers, we'd need reactor/reactor-netty#218.