Add Epsilon- and Eta-Sampling
# What does this PR do?

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Implements epsilon- and eta-sampling, as seen in [[Truncation Sampling as Language Model Desmoothing](https://arxiv.org/abs/2210.15191)](https://arxiv.org/abs/2210.15191). The code is adapted from the author's official repository [here](https://github.com/john-hewitt/truncation-sampling).

Resolves #21092.


## Before submitting
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- [x] Did you write any new necessary tests?


## Who can review?

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Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts and @NielsRogge
- speech models: @sanchit-gandhi

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @sgugger

Integrations:

- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam

Documentation: @sgugger, @stevhliu and @MKhalusova

HF projects:

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

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: @sgugger
- TensorFlow: @Rocketknight1

 -->
@gante

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_21121). All of your documentation changes will be reflected on that endpoint.<|||||>@gante I incorporated your changes! I rebased with `main` because there were some merge conflicts, which caused some of the review snippets above to get "outdated," but it's done!<|||||>@sgugger this PR adds a new sampling-based generation strategy that can be effectively implemented through logits processors<|||||>Yeah, no problem!😊<|||||>@shermansiu now step 4 remains :) Would you like to work on it? (we can retweet and share your posts)<|||||>I'm interested, but it feels like it's best added to https://github.com/huggingface/blog/blob/main/notebooks/02_how_to_generate.ipynb than in its own notebook, as other truncation sampling approaches (top-p and top-k) are already there.<|||||>We don't update the notebooks for our blog posts, so they stay consistent with their content :) But we will certainly update our [new docs](https://huggingface.co/docs/transformers/main/en/generation_strategies)

The new docs only contain simple examples (for now), so the benefits of the new generation strategy should be showcased in a notebook. In the near future, we will have an advanced text generation doc with clear examples for each flag (but it won't be ready in the next 2-3 months)<|||||>I have a lot on my to-do list right now... Although I'd love to contribute to the notebook, I think it's unrealistic for me to be able to put something out soon.<|||||>Yesterday's ACL 2023 tutorial on "Generating Text from Large Language Models" covers eta-sampling and more! John Hewitt, the first author of the eta-sampling paper, was one of the presenters for that tutorial!

Site: https://rycolab.io/classes/acl-2023-tutorial/
Slides: https://drive.google.com/file/d/1UHbGcjzBURG1n2DufC7iDTmGNjIz5Dp_/view