Support SocketAddress for proxies

[AlexProgrammerDE]

Currently proxies are required to be InetSocketAddress, but netty allows any SocketAddress to be used as a proxy.
This can be seen in in the ProxyProvider class:

reactor-netty/reactor-netty-core/src/main/java/reactor/netty/transport/ProxyProvider.java

Line 429 in ed7c964

public final Builder address(Supplier<? extends InetSocketAddress> addressSupplier) {

Motivation

I'm interested in using UnixDomainSocket for proxies instead of InetSocketAddress.

Desired solution

Extend the functionality of the proxy provider class to allow passing a SocketAddress instead of a InetSocketAddress to a proxy.
I've made a rough example how that could be made in a fork of mine: AlexProgrammerDE@a76c01d
It tries to keep backwards support until the next major release is made.
I'd recommend the maintainers use my commit as a reference.

Considered alternatives

Support UnixDomainSocket instead, but it's probably easier to just support SocketAddress directly to allow other future implementations of that class.

[violetagg]

@AlexProgrammerDE Are you interested in providing a PR? Which Reactor Netty version should enable this feature (1.1.x or 1.2.x)?

[AlexProgrammerDE]

Opened at #3243
I think 1.2.x works.