Named formatting options in filename argument is broken when it contains "/"
🐛 Bug / Limitation

I think this might be a limitation instead of a bug.
Named formatting options in filename argument is broken when it contains "/". "/" is used because I want to group different metrics.
From pytorch documentation

Lots of information can be logged for one experiment. To avoid cluttering the UI and have better result clustering, we can group plots by naming them hierarchically. For example, “Loss/train” and “Loss/test” will be grouped together, while “Accuracy/train” and “Accuracy/test” will be grouped separately in the TensorBoard interface.

for example, if I want to save my model using xx/iou metric, I wil do something like the following
trainer_config = {}
checkpoint_callback = ModelCheckpoint(
      monitor='xx/iou',
      dirpath="/path/to/dir",
      filename='my_model_{epoch:02d}_{xx/iou:.2f}',
      save_top_k=5,
      mode='max',
  )
trainer_config["callbacks"] = [checkpoint_callback]
trainer = pl.Trainer(**trainer_config)

I would expect models are saved with names like /path/to/dir/my_model_epoch=123_iou=80.ckpt but the slash in "xx/iou" causes some trouble. The checkpoint file is actually saved to "/path/to/dir/my_model_epoch=123_xx" directory with the name iou=80.ckpt.
Since "/" is not allowed in filenames in linux, I think maybe xx/iou should be updated to xx_iou to work around the issue ?
Environment
pytorch-lightning      1.1.2
python 3.6.9