[Testing] Add Flax Tests on GPU, Add Speech and Vision to Flax & TF tests
# What does this PR do?

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This PR does two things:
- 1. Adds Flax to the daily slow tests on GPU and adds flax tests on GPU. There is a TF Docker image that works well for JAX on GPU - see: https://github.com/google/jax/discussions/6338 . I think it's easiest to just use this image for now until there is an official JAX docker image for GPU.
- 2. We now have slow tests in both TF and Flax that require `soundfile` (TFHubert, TFWav2Vec2, FlaxWav2Vec2, ... Also there is FlaxViT in Flax which requires the `vision` package IMO. A new `tf-flax-speech` extension is added to make sure one doesn't install torch along torchaudio for TF and Flax's speech models and it is added to all the tests.


Also it is very likely that some slow tests in Flax will fail at the moment since they have been written to pass on TPU. If ok, @patil-suraj and I can fix them one-by-one after getting a report from the daily slow tests - we'll probably have to add some `if-else` statements depending on the backend there... 
2nd, at the moment, we don't have any multi-GPU or multi-TPU tests for Flax, but I nevertheless enable the tests on multi-gpu on Flax here already. I'll add a multi-gpu/multi-tpu test for all flax models next week (cc @patil-suraj)

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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
- research_projects/bert-loses-patience: @JetRunner
- research_projects/distillation: @VictorSanh

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> Looks great! Mostly left nitpicks. I'm fine with seeing which tests failed on a first run and then adapting/removing failed tests.
> 
> Do you have a number in mind regarding total runtime?

All non-slow tests together took 1h20, we don't have that many slow tests in Flax at the moment - so I'd assume that the total runtime would be something like 1h40<|||||>Running all the jitted tests takes a lot of time (but they're quite important IMO) <|||||>Ok sounds good!