[tensorboard][writer] Add missing 'dataformats' argument to 'add_image' docs.
The [torch.utils.tensorboard.SummaryWriter.add_image](https://pytorch.org/docs/stable/_modules/torch/utils/tensorboard/writer.html#SummaryWriter.add_image) is missing the argument `dataformats` in the docs.
This PR adds the missing argument to the docs (analogous to `add_images` docs).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48834
Approved by: https://github.com/ezyang
