Add a separate quantitative eval nb

[hemajv]

In this PR, the following changes are being made:

• Updated https://github.com/redhat-et/api-docs-generation/blob/main/notebooks/evaluation/evaluation_metrics.ipynb to remove the quantitative evaluation section (moving this to a separate notebook)
• A separate quantitative evaluation notebook with more prompt examples added
• Included a helper_functions.ipynb notebook
• Updated utils.py with the modified prompt for evaluating the output using GPT

(related to #24)

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[oindrillac]

Thanks for the updates @hemajv LGTM