Examples: add Bloom support for token classification
Hi,

this PR adds support for fine-tuning Bloom models for token classification tasks.

After trying out the current example, I got an error message from the tokenizer part, that `add_prefix_space=True` needs to be set. So with this PR, Bloom can be used in token classification example for PyTorch (there's no support for TensorFlow/FLAX yet).
_The documentation is not available anymore as the PR was closed or merged._<|||||>cc @younesbelkada <|||||>Hi @younesbelkada ,

sure no problem, here are the steps (fresh environment):

```bash
git clone https://github.com/huggingface/transformers.git
cd transformers/
pip3 install -e .
pip3 install seqeval evaluate
cd examples/pytorch/token-classification
python3 run_ner.py   --model_name_or_path bigscience/bloom-560m   --dataset_name conll2003   --output_dir ./output-bloom-560m   --do_train   --do_eval   --do_predict
```

Then the following error message is thrown:

```bash
Traceback (most recent call last):
  File "run_ner.py", line 630, in <module>
    main()
  File "run_ner.py", line 464, in main
    train_dataset = train_dataset.map(
  File "/opt/conda/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 2387, in map
    return self._map_single(
  File "/opt/conda/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 557, in wrapper
    out: Union["Dataset", "DatasetDict"] = func(self, *args, **kwargs)
  File "/opt/conda/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 524, in wrapper
    out: Union["Dataset", "DatasetDict"] = func(self, *args, **kwargs)
  File "/opt/conda/lib/python3.8/site-packages/datasets/fingerprint.py", line 480, in wrapper
    out = func(self, *args, **kwargs)
  File "/opt/conda/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 2775, in _map_single
    batch = apply_function_on_filtered_inputs(
  File "/opt/conda/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 2655, in apply_function_on_filtered_inputs
    processed_inputs = function(*fn_args, *additional_args, **fn_kwargs)
  File "/opt/conda/lib/python3.8/site-packages/datasets/arrow_dataset.py", line 2347, in decorated
    result = f(decorated_item, *args, **kwargs)
  File "run_ner.py", line 422, in tokenize_and_align_labels
    tokenized_inputs = tokenizer(
  File "/workspace/transformers/src/transformers/tokenization_utils_base.py", line 2475, in __call__
    encodings = self._call_one(text=text, text_pair=text_pair, **all_kwargs)
  File "/workspace/transformers/src/transformers/tokenization_utils_base.py", line 2561, in _call_one
    return self.batch_encode_plus(
  File "/workspace/transformers/src/transformers/tokenization_utils_base.py", line 2752, in batch_encode_plus
    return self._batch_encode_plus(
  File "/workspace/transformers/src/transformers/models/bloom/tokenization_bloom_fast.py", line 140, in _batch_encode_plus
    raise Exception(
Exception: You need to instantiate BloomTokenizerFast with add_prefix_space=True to use it with pretokenized inputs.
```