Add remote and/or local addresses for unix domain socket

This is split out of #9900, which had two pieces. See it for more details. CC @carl-mastrangelo

Unix domain sockets are strange from a local/remote address perspective, as only one of them generally has a well-defined name (file path). We need to see what other languages do, but at the very least for this to be considered completed we should have _one_ of local/remote for both client and server.

Right now apparently the code is missing both, when using KQueue or Epoll, as Netty is not providing either:
```
{io.grpc.internal.GrpcAttributes.securityLevel=NONE, io.grpc.Grpc.TRANSPORT_ATTR_REMOTE_ADDR=null, io.grpc.Grpc.TRANSPORT_ATTR_LOCAL_ADDR=null}
```

We might consider enhancing Netty, but that'd probably take some double-checking in how Linux itself handles this. If we think we can't even add addresses (because we find that Netty did it that way "for a good reason"), we need an attribute of some sort to identify UDS connections, so absolute worst-case would be a SocketAddress that just said "this is a UDS connection" without any other information.

Inizia dall’issue #9900 per il contesto originale, quindi esamina come i percorsi KQueue ed Epoll espongono gli attributi di trasporto di Netty. Analizza come Netty e Linux rappresentano gli indirizzi dei socket di dominio Unix, incluso il comportamento del client e del server. Il lavoro è completo quando sia il client sia il server espongono almeno un indirizzo locale o remoto, oppure una SocketAddress che identifichi chiaramente un UDS quando non è possibile fornire gli indirizzi.

Scritto dal modello di indicizzazione a partire dal testo della issue.