Add initial UDS stream implementation

[iksaif]

This PR adds experimental support for UDS streams, which can be used by using DD_DOGSTATSD_URL=unixstream:///path/to/dsd.sock or the following code:

    Callable<SocketAddress> addressLookup = new Callable<SocketAddress>() {
            @Override
            public SocketAddress call() throws Exception {
                return new UnixSocketAddressWithTransport(new UnixSocketAddress("/path/to/dsd.sock"), UnixSocketAddressWithTransport.TransportType.UDS_STREAM));
            }
        };

        client = new NonBlockingStatsDClientBuilder().prefix("my.prefix")
            .addressLookup(addressLookup)
            .port(0)
            .build();

Before this transport becomes GA we should revisit the builder to make it easier to use.

The telemetry will behave exactly like the go client with DataDog/datadog-go#290
If unix:// is used or TransportType.UDS we still default to SOCK_DGRAM and do not try to guess the socket type (yet) as this isn't trivial with the current code structure (in particular when we create the client before the socket exists)

[blt]

I find it a little strange that none of the gitlab CI appears to have fired. Worthwhile to push an empty commit, or rebase from main, in case gitlab was broken at the branch point of this PR.

[iksaif]

I find it a little strange that none of the gitlab CI appears to have fired. Worthwhile to push an empty commit, or rebase from main, in case gitlab was broken at the branch point of this PR.

We don't have gitlab CI for this project

[iksaif]

I think I addressed everything but give me some time to validate that the tests are not flakky

[vickenty]

Small nits about comments, but otherwise LGTM