[dynamo] Add ddp_graphs artifact (#100021)
I want to be able to decouple DDP graph printing from the rest of
dynamo DEBUG-level logging, since frequently these logs are particularly
enlightening.
Differential Revision: [D45290919](https://our.internmc.facebook.com/intern/diff/D45290919/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100021
Approved by: https://github.com/wconstab, https://github.com/mlazos
