add code samples for TF speech models
# What does this PR do?

Add:

- TF_SPEECH_BASE_MODEL_SAMPLE
- TF_SPEECH_CTC_SAMPLE

I tested them manually with TFWav2Vec2 (not through doctest).


## Remark:

The following samples are not translated to TF, since I couldn't find models like `TFWav2Vec2ForSequenceClassification`.

- PT_SPEECH_SEQ_CLASS_SAMPLE,
- PT_SPEECH_FRAME_CLASS_SAMPLE,
- PT_SPEECH_XVECTOR_SAMPLE,
_The documentation is not available anymore as the PR was closed or merged._