[Metricbeat] Adding AWS ELB Metricset

[kaiyan-sheng]

Elastic Load Balancing reports metrics to CloudWatch only when requests are flowing through the load balancer. If there are requests flowing through the load balancer, Elastic Load Balancing measures and sends its metrics in 60-second intervals. If there are no requests flowing through the load balancer or no data for a metric, the metric is not reported.

Please see more details and a list of available metrics in:
https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-cloudwatch-metrics.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:

• Supported versions are documented
• Supported operating systems are documented (if applicable)
• 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