cmd/serve: add serve docker command (#5415)

Fixes #4750

Co-authored-by: Ivan Andreev <ivandeex@gmail.com>

cmd/serve/docker/unix_unsupported.go

@@ -0,0 +1,12 @@
+// +build !linux,!freebsd
+
+package docker
+
+import (
+	"errors"
+	"net"
+)
+
+func newUnixListener(path string, gid int) (net.Listener, string, error) {
+	return nil, "", errors.New("unix sockets require Linux or FreeBSD")
+}