fix for generation that never stops in Llama3-Instruct variants (#1904)

* fix for loading of special tokens in Llama tokenizer

* fix for Llama tokenizer which can have multiple end tokens

* bug fix

* adding some missing tokens to Llama3 tokenizer

* fixed tests and Llama3Tokenizer init.

* now loading correct eos_token config from Hugging Face checkpoint. Using hack for Keras checkpoint because it does not have this info

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Co-authored-by: Martin Görner <[email protected]>

Author: martin-gorner