feat(server/client): add windows pipe, pipe peer credentials support

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

creds/peercreds/peercreds_unix.go

@@ -0,0 +1,20 @@
+//go:build !windows
+
+package peercreds
+
+import (
+	"net"
+
+	"github.com/tailscale/peercred"
+)
+
+func Get(conn net.Conn) (*Creds, error) {
+	creds, err := peercred.Get(conn)
+	if err != nil {
+		return nil, err
+	}
+	var c Creds
+	c.uid, _ = creds.UserID()
+	c.pid, _ = creds.PID()
+	return &c, nil
+}