Fail quickly when the dataset card contains `viewer: false`
The Hub shows a specific message, instead of the dataset viewer, when the dataset card contains the metadata `viewer: false`.

I think that we should take it into account when checking if a dataset is supported, and fail fast (adding this case in https://github.com/huggingface/datasets-server/blob/main/libs/libcommon/src/libcommon/dataset.py#L165, along to checking if the dataset is private) 
Fail quickly when the dataset card contains `viewer: false`: The Hub shows a specific message, instead of the dataset viewer, when the dataset card contains the metadata `viewer: false`.

I think that we should take it into account when checking if a dataset is supported, and fail fast (adding this case in https://github.com/huggingface/datasets-server/blob/main/libs/libcommon/src/libcommon/dataset.py#L165, along to checking if the dataset is private) 