[Metricbeat] Adding AWS EBS Metricset

[kaiyan-sheng]

Amazon Elastic Block Store (Amazon EBS) sends data points to CloudWatch for several metrics. Data is only reported to CloudWatch when the volume is attached to an instance.
A list of AWS EBS metrics from Cloudwatch: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/monitoring-volume-status.html

Metricbeat Module / Dataset release checklist

This checklist is intended for Devs which create or update a module to make sure modules are consistent.

Modules

For a metricset to go GA, the following criterias should be met:

• Integration tests exist
• System tests exist
• Automated checks that all fields are documented
• Documentation
• Fields follow ECS and naming conventions
• Dashboards exists (if applicable)

Metricbeat module

• Example data.json exists and an automated way to generate it exists (go test -data)
• Test environment in Docker exist for integration tests