This is a common problem that can easily be fixed by Tesla service. It has to do with the mounting points between the steering rack and the car's frame. The current engineering design has minimal surface area at these mounting points. When you turn the steering wheel while the car is stationary, significant lateral force is applied across these mounts, causing the two surfaces to rub against each other, creating the clicking sound. It is by no means dangerous. The fix involves a shim and a special grease.
This is not the same issue as the drive train click or clunk when starting up from a stop.