`ORIGINAL_CHANNEL_DIM` datatype for collate

[wyli]

Describe the bug
the ORIGINAL_CHANNEL_DIM field currently allows different datatypes

MONAI/monai/data/image_reader.py

Lines 307 to 309 in 68074f0

	header[MetaKeys.ORIGINAL_CHANNEL_DIM] = (
	"no_channel" if len(data.shape) == len(header[MetaKeys.SPATIAL_SHAPE]) else -1
	)

and this causes errors when collating multiple metatensors:

MONAI/monai/data/utils.py

Line 436 in 68074f0

collated.meta = default_collate([i.meta or TraceKeys.NONE for i in batch])

>>> from monai.data import MetaTensor
>>> a = MetaTensor(1, meta={"original_channel_dim": 1})
>>> b = MetaTensor(1, meta={"original_channel_dim": "no_channel"})
>>> from monai.data import list_data_collate
>>> list_data_collate([a,b])
> collate/stack a list of tensors
Traceback (most recent call last):
  File "/usr/local/anaconda3/envs/py38/lib/python3.8/site-packages/torch/utils/data/_utils/collate.py", line 128, in collate
    return elem_type({key: collate([d[key] for d in batch], collate_fn_map=collate_fn_map) for key in elem})
  File "/usr/local/anaconda3/envs/py38/lib/python3.8/site-packages/torch/utils/data/_utils/collate.py", line 128, in <dictcomp>
    return elem_type({key: collate([d[key] for d in batch], collate_fn_map=collate_fn_map) for key in elem})
  File "/usr/local/anaconda3/envs/py38/lib/python3.8/site-packages/torch/utils/data/_utils/collate.py", line 120, in collate
    return collate_fn_map[elem_type](batch, collate_fn_map=collate_fn_map)
  File "/usr/local/anaconda3/envs/py38/lib/python3.8/site-packages/torch/utils/data/_utils/collate.py", line 184, in collate_int_fn
    return torch.tensor(batch)
TypeError: new(): invalid data type 'str'

cc @holgerroth