[examples/flax] clip style image-text training example
# What does this PR do?

This PR adds an example script to train CLIP style vision-text dual encoder models using pre-trained vision and text encoder.
It supports `CLIP` and `ViT` as image encoder and `BERT` and ROBERTa` (or any other text encoder in flax) as text encoder.

This example uses`torchvision` and torch `Dataloader` for faster pre-processing and data loading. This is important as data loading and processing can become a bottleneck on TPU. This will be revised later to use `datasets`.
And think you might have to run `make style` once<|||||>Merging!<|||||>hi @patil-suraj i tried to run your script(run_hybrid_clip.py)

after few step i got error

```
it/s/home/acul/env/lib/python3.8/site-packages/transformers/tokenization_utils_base.py:699: VisibleDeprecationWarning: Creating an ndarray from ragged nested sequences (which is a list-or-tuple of lists-or-tuples-or ndarrays with different lengths or shapes) is deprecated. If you meant to do this, you must specify 'dtype=object' when creating the ndarray.
  tensor = as_tensor(value)
Epoch ... (1/40):   0%|                                                | 0/40 [02:43<?, ?it/s]
Traceback (most recent call last):                           | 39/462 [02:43<06:48,  1.03it/s]
  File "run_hybrid_clip.py", line 556, in <module>
    main()
  File "run_hybrid_clip.py", line 502, in main
    state, train_metric = p_train_step(state, batch)
  File "/home/acul/env/lib/python3.8/site-packages/jax/_src/traceback_util.py", line 183, in reraise_with_filtered_traceback
    return fun(*args, **kwargs)
  File "/home/acul/env/lib/python3.8/site-packages/jax/_src/api.py", line 1623, in f_pmapped
    for arg in args: _check_arg(arg)
  File "/home/acul/env/lib/python3.8/site-packages/jax/_src/api.py", line 2296, in _check_arg
    raise TypeError(f"Argument '{arg}' of type {type(arg)} is not a valid JAX type.")
jax._src.traceback_util.UnfilteredStackTrace: TypeError: Argument '[[list([1, 1, 1, 1, 
.
.
.
.
  list([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])]]' of type <class 'numpy.ndarray'> is not a valid JAX type.

```
i use [bert](https://huggingface.co/indobenchmark/indobert-base-p1) and clip as model vision and text

any idea how to fix<|||||>Thank you for reporting! 
Could you please open an issue and post the command that you used?<|||||>sure 

opening here:
https://github.com/huggingface/transformers/issues/12502