Allow fine-tune wav2vec2 with local path custom dataset
# What does this PR do?

In the examples for fine-tuning Wav2Vec2 it is possible to use a HuggingFace dataset that is ready to be trained. But when we want to use a local/custom dataset, it's easier to create a .tsv that points to the file path. Which doesn't work in current version - returning error: "AttributeError: 'Value' object has no attribute 'sampling_rate'"

So this PR adds a code to check if the "audio_column_name" has an audio format or a path (string), if it is a string, load the file and convert it to audio format.

Below is an example of a .tsv file that does not work with the current version and works with this PR:

path | sentence
-- | --
data/clips/common_voice_tr_21921195.mp3 | Pirin sözleri hâlâ yankılanıyor.
data/clips/common_voice_tr_21921199.mp3 | Müze Gecesi beş yıldır her yıl düzenleniyor.
data/clips/common_voice_tr_21921206.mp3 | Yunanistan'ın Selanik kenti de ilk ona girdi.


## Who can review?

@sanchit-gandhi



@ProgramadorArtificial Thanks for taking the time to open this PR. 

The example scripts are just examples and won't work out-of-the-box for all problems. As you've done here, a few lines of code might be needed to adapt to different use cases. This change is very specific. As such, it's not an addition we'll be merging in.  
<|||||>Hey @ProgramadorArtificial! In this case, it might be easier to first load your audio data as a HF datasets object (here's an excellent guide on how to do so: https://huggingface.co/docs/datasets/audio_load). You can then save this data locally and/or push it to the Hub:
```python
# set a save path and HF Hub dataset id
LOCAL_DATASET_DIR = ...
HF_DATASET_ID = ...

dataset.save_to_disk(LOCAL_DATASET_DIR)
# and/or push to hub
dataset.push_to_hub(HF_DATASET_ID)
```
You'll then be able to use the training script directly with your dataset (either from the local path or loading from the Hub, in the same way that we do for Common Voice in the example).<|||||>Hey @ProgramadorArtificial - just re-iterating that the examples script is assumed to work with a HF dataset that has an audio column already present (i.e. one that has an [`Audio` feature](https://huggingface.co/docs/datasets/v2.12.0/en/package_reference/main_classes#datasets.Audio)). If your custom dataset does not have the audio files loaded up, you'll need to perform a round of pre-processing to get your dataset into the right format for this script (expected to have two columns: "audio" and "text").