feat: update evaluation flow sample for abstractive summarization with g-eval method to enable GPT-4-Turbo

[fujikosu]

Description

This PR updates a evaluation flow example that was introduced by #2037. This example only supported GPT-4 previously as GPT-4-Turbo was showing poor performance with previous approach. With this update, GPT-4-Turbo is introduced and meta-evaluated along with the implementation update from sampling based approach to weighted average over probability approach. New implementation outperformed previous evaluation performance according to meta-evaluation result. Besides, this new approach reduces estimated cost of evaluation from $6.19 to $1.32 per 100 documents.

Previous approach is still kept under sampling_based directory to provide backward compatibility with GPT-4 evaluator and reference for meta-evaluation

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