Switch TORCH_TRACE to accept a directory by default (#121331)
Directory is better because it works smoothly with distributed
runs; otherwise you'd need to modify torchrun to setup distinct
log names for each file.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Differential Revision: [D54597814](https://our.internmc.facebook.com/intern/diff/D54597814)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121331
Approved by: https://github.com/albanD
