[`Speech-Encoder-Decoder`] Add `speech-encoder-decoder` to `AutoProcessor`
# What does this PR do?

Currently loading the correct processor for `speech-encoder-decoder` using `AutoProcessor` is broken on `main`. 
The issue and the fix is very identical as https://github.com/huggingface/transformers/pull/21299 , as a doctest was also failing. Link to failing job: https://github.com/huggingface/transformers/actions/runs/4002271138/jobs/6869333719 

cc @ydshieh @sgugger 

Hi @younesbelkada ! Thank you for the PR(s). In my opinion, (generic) composite models like (text/vision/speech) encoder-decoder models are not meant to use `Auto` mappings, as their design is to compose any pair of models (whenever it works).

The fix should be updating the config file on the hub for these checkpoints. In this case, by adding `processor_class`, for which I have opened those Hub PR.<|||||>Makes sense! Thanks for explaining! <|||||>_The documentation is not available anymore as the PR was closed or merged._