Add Support For Unix Domain Sockets

It would be nice if this logger would support Unix Domain Sockets as the target instead of only (host, port) inet addresses. `UnixDomainSocketAddress` was added in Java 16. However, this library need not depend on that if `SocketAddress` can be supplied to `getLogger()` which has been around since 1.4.

This feature would be particularly useful for container environments such as Docker because some not very nice tricks are required for a container to connect to a host socket. Note that Unix domain sockets are supported by [Fluentd](https://docs.fluentd.org/input/unix) and [Fluent-Bit](https://docs.fluentbit.io/manual/pipeline/inputs/forward).

Start by reading the getLogger() entry point and tracing how the current (host, port) inet address is handled. Look for existing tests around logger targets; done means a SocketAddress can represent a Unix domain socket and messages can be sent to it, with coverage for the new path.

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