Fix InferenceAPI on image task

[Wauplin]

Related to slack discussion (internal link).

• text-to-image now works by returning a Pillow image (if PIL is installed, otherwise you get an ImportError).
• if content type is application/json or image/jpeg => we parse the output. Otherwise raise NotImplementedError. This is in particular the case for text-to-speech tasks.
• the InferenceAPI has now a kwarg raw_response: bool = False. If True, we return the full Response object to the user. At least this way if we don't handle a task yet, the user can build its own parser (typically for audio).
• adapted/fixed some stuff (now sending user agent in request for example)
• => added 2 examples in the doc and some tests

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[osanseviero]

LGTM!

[codecov]

Codecov Report

Base: 82.26% // Head: 83.90% // Increases project coverage by +1.63% 🎉

Coverage data is based on head (7ceef22) compared to base (d147cbd).
Patch coverage: 76.19% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1270      +/-   ##
==========================================
+ Coverage   82.26%   83.90%   +1.63%     
==========================================
  Files          47       47              
  Lines        4596     4609      +13     
==========================================
+ Hits         3781     3867      +86     
+ Misses        815      742      -73     

Impacted Files	Coverage Δ
src/huggingface_hub/utils/__init__.py	100.00% <ø> (ø)
src/huggingface_hub/utils/_runtime.py	62.38% <60.00%> (-0.12%)	⬇️
src/huggingface_hub/inference_api.py	90.90% <81.25%> (+2.02%)	⬆️
src/huggingface_hub/repository.py	78.76% <0.00%> (+13.27%)	⬆️

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[Wauplin]

Thanks for the review @osanseviero ! I've added the docstring and will now merge :)