Add metrics for translation and summarization (BLEU, ROUGE, BLEURT, BERTSCORE, COMETKIWI, Perplexity)

[myeongho-jeong-yanolja]

1. Add various metrics such as ROUGE, BERTSCORE, BLEURT, etc. Reference-based metrics
   • BLEU, ROUGE - N-gram based matching
   • BERTSCORE - Embedding similarity with BERT
   • BLEURT - Training human prediction for evaluation Reference-free metrics
   • COMETKIWI - Sentence-level / Word-level comparison between predicted and source with LM
   • Perplexity - how well a model predicts a our domain text sequence
2. make efficient when we calculate metrics (Calculate score in aggregation step - metric is called for every sample!)

I'll update README.md soon.

[seungduk-yanolja]

Please update the PR title to describe briefly what metrics they are. E.g., Add metrics for translation and summarization