[Speech Examples] Add new audio feature
Author: patrickvonplaten
Pull request: yes

# What does this PR do?

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This PR refactors the speech example scripts to use the new audio feature.

cc @anton-l - I think more or less the same can be used for the audio classification script


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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
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HF projects:

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Comments:
Maybe also cc @lhoestq @albertvillanova to see how we'd like to use the audio feature