add query stats to logs | fix np encoding for logs JSON dump

[sureshkumarsrinath]

• This PR fixes the issue what json dump was not able to comprehend the numpy datatypes produced by FAISS, ranker and embeddings by converting them to primitive type in Python
• The times of chunk retrieval, ranking, query generation are collected and logged.

TODO: Keep only the required information in the logs and remove the rest of the components in the log JSON object

credits: https://github.com/sukriti112

[RajShah-1]

I think some of these items are also being addressed in: #75.