Properly use Reactor Netty 2 in `AbstractHttpHandlerIntegrationTests`

[sdeleuze]

[sdeleuze]

When using properly ReactorNetty2HttpServer, we get some multipart related errors due to an additional EOL that does not appear on other servers, could be due to a bug in Netty 5. While checking the latest version, I saw that the latest release for Netty 5 is still 5.0.0.Alpha5 release in September 2022. I will ping Reactor team about that.