Add server.netty.max-keep-alive-requests

[philsttr]

A new maxKeepAliveRequests property was added to the http server in reactor-netty v1.0.13 (reactor/reactor-netty#1865 / reactor/reactor-netty#1867)

It would be great if spring boot allowed the maxKeepAliveRequests to be configured via a server.netty.max-keep-alive-requests property, similar to the other reactor-netty server properties.

[philwebb]

Closing in favor of PR #28875. Thanks @polarbear567!