Metric Stream cost calculation

[Azanul]

Problem

Issue #878

Solution

metric stream cost = update cost * no. of updates

Fetching MetricUpdate cost using pricing API and update count using cloudwatch statistics API.

ref:

• CloudWatch-metric-streams-monitoring
• CloudWatch Pricing

Changes Made

• Added function for fetching pricePerUnit from GetProductsOutput.
• Added cost calculation for Metric Streams.
• Fixes Add Cost Calculation for AWS Cloudwatch Log Metrics #878

Notes

• Ignored the AWS Kinesis Data Firehose surcharge

Checklist

• Code follows the contributing guidelines
• Changes have been thoroughly tested
• Documentation has been updated, if necessary
• Any dependencies have been added to the project, if necessary

Reviewers

@mlabouardy
@ShubhamPalriwala

[mlabouardy]

Thanks @Azanul for the PR. I requested a small change before merging the PR :)

[mlabouardy]

LGTM!