Add `torch.compile` guide to docs

[carmocca]

📚 Documentation

This applies to

• Fabric (Compile guide for Fabric #19330)
• PyTorch Lightning

Things to mention:

• Compiling nn.Module vs LightningModule or fabric.setup(module) (Clarify where to apply torch.compile in Fabric and add more tests #17250)
• Known limitations.
• Known sources of graph breaks.

Related: #12398

cc @Borda @carmocca @justusschock @awaelchli

[awaelchli]

This would also close #17250