[Hubert] Fix Hubert processing auto
# What does this PR do?

Currently on the `main` branch, the scripts provided on the docstring of `Hubert` fails:
```
from transformers import AutoProcessor, HubertModel
from datasets import load_dataset
import soundfile as sf

processor = AutoProcessor.from_pretrained("facebook/hubert-large-ls960-ft")
model = HubertModel.from_pretrained("facebook/hubert-large-ls960-ft")

def map_to_array(batch):
  speech, _ = sf.read(batch["file"])
  batch["speech"] = speech
  return batch

ds = load_dataset("hf-internal-testing/librispeech_asr_dummy", "clean", split="validation")
        
ds = ds.map(map_to_array)

input_values = processor(ds["speech"][0], return_tensors="pt").input_values  # Batch size 1
hidden_states = model(input_values).last_hidden_statehidden_states = model(input_values).last_hidden_state
```
With the PR #21225 all custom `xxxProcessor` have been removed in favor of `AutoProcessor` in docstrings. Since `Hubert` was not included inside the processor automapping the script above lead into a bug, since if the model is not present in the auto mapping dictionary, the script will try to load a tokenizer: https://github.com/huggingface/transformers/blob/255257f3ea0862cbb92ea9fa1113cbee1898aadd/src/transformers/models/auto/processing_auto.py#L275 / Hence, `Wav2vec2CTCTokenizer` was loaded instead of `Wav2vec2Processor` that is supposed to be the target object to be loaded.

This PR fixes this by adding `hubert` inside the automapping class for `AutoProcessor`

This PR also fixes 2 failing doctests for `HubertModel`, link to failing job: https://github.com/huggingface/transformers/actions/runs/4002271138/jobs/6869333719

cc @sgugger @ydshieh 
_The documentation is not available anymore as the PR was closed or merged._<|||||>Thanks!