NetBird SSH (#361)

This PR adds support for SSH access through the NetBird network
without managing SSH skeys.
NetBird client app has an embedded SSH server (Linux/Mac only) 
and a netbird ssh command.

client/ssh/window_unix.go

@@ -0,0 +1,14 @@
+//go:build linux || darwin
+
+package ssh
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+func setWinSize(file *os.File, width, height int) {
+	syscall.Syscall(syscall.SYS_IOCTL, file.Fd(), uintptr(syscall.TIOCSWINSZ), //nolint
+		uintptr(unsafe.Pointer(&struct{ h, w, x, y uint16 }{uint16(height), uint16(width), 0, 0})))
+}