Enable Training on Apple Silicon Processors in PyTorch

With the release of PyTorch 1.12 in May of this year, PyTorch added experimental support for the Apple Silicon processors through the Metal Performance Shaders (MPS) backend. If you own an Apple computer with an M1 or M2 chip and have the latest version of PyTorch installed, you can now train models faster. Even better news: in the latest 1.7 release of PyTorch Lightning, we made it super easy to switch to the MPS backend without any code changes! Support for this accelerator is currently marked as experimental in PyTorch. Because many operators are still missing, you may run into a few rough edges. PyTorch and Lightning will continue to improve support for Apple Silicon, so stay tuned for future releases!