SpringBoot Enable netty leak detector

Motivation:

detect Netty resource leaks using Netty's paranoid leak detector

Modifications:

• add Netty leak detector junit library
• enable junit extension on NettyReactiveWebServerFactoryTests

Result:

NettyReactiveWebServerFactoryTests will check for netty leaks

Comment From: wilkinsona

Thanks for the proposal. I don't think Boot is the right place for this low-level leak detection and it's better done in the library, Reactor Netty, that's interacting with Netty directly. Reactor Netty is already tested with leak detection enabled so I think we're already covered here.