Problem
Use the insurance dataset to finish the following questions:
1) Show the number of documents in the collection using Aggregation.
2) Only select fields - bmi, smoker, from the collection and only display 5 documents in the output.
3) Show the number of documents who is a "smoker" with age larger than 30.
4) Show the average charges for each region.
5) Show the average charges for records with different number of children excluding those without children (children = 0).
6) Show the average (charges+100) for records with different number of children excluding those without children (children = 0).