Do not log the generation config for each prediction step in TrainerSeq2Seq
Author: regisss
Pull request: yes

# What does this PR do?

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`generation_config` is currently initialized every time `generate` is called with `generation_config=None` (see [here](https://github.com/huggingface/transformers/blob/98d88b23f54e5a23e741833f1e973fdf600cc2c5/src/transformers/generation/utils.py#L1183)). This will also log the generation config (see [here](https://github.com/huggingface/transformers/blob/98d88b23f54e5a23e741833f1e973fdf600cc2c5/src/transformers/generation/configuration_utils.py#L557)). Therefore, it will be logged for each iteration of the evaluation loop of `TrainerSeq2Seq`.
To avoid this behavior, this PR introduces a hack that sets `self.model.generation_config._from_model_config` to `False` after the first call to `generate` in `TrainerSeq2Seq` to ensure that 1) the right generation config has been initialized, 2) it will not be initialized in the following interations.

Internal discussion [here](https://huggingface.slack.com/archives/C01N44FJDHT/p1675159917133549).


## Before submitting
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## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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Models:

- text models: @ArthurZucker and @younesbelkada
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Library:

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- tokenizers: @ArthurZucker
- trainer: @sgugger

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HF projects:

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