[Metricbeat] Create ebs metricset using light module

[kaiyan-sheng]

This PR is to use #12465 to create ebs metricset for aws. ebs metricset collects metrics from aws cloudwatch with namespace AWS/EBS using aws module cloudwatch metricset.

Amazon Elastic Block Store (Amazon EBS) sends data points to CloudWatch for several metrics. Amazon EBS General Purpose SSD (gp2), Throughput Optimized HDD (st1) , Cold HDD (sc1), and Magnetic (standard) volumes automatically send five-minute metrics to CloudWatch. Provisioned IOPS SSD (io1) volumes automatically send one-minute metrics to CloudWatch. Data is only reported to CloudWatch when the volume is attached to an instance. Please see https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using_cloudwatch_ebs.html for more details on each metric.

For ebs metricset, default collection period is set to 5min with Average/Sum as statistic method.
Overview dashboard:

closes #11699

How to test this:

1. Make sure the AWS environment you are using for testing has EBS, which is a part of EC2. So to check if your environment has volumes, go to EC2 service and then click Volues on the left side under ELASTIC BLOCK STORE: https://console.aws.amazon.com/ec2/v2/home?region=us-east-1#Volumes:sort=desc:createTime
2. Make sure AWS credentials are correct and valid in ~/.aws/credentials under profile test-mb
3. Download Metricbeat and enable aws module: ./metricbeat modules enable aws
4. Change aws.yml to enable ebs metricset:

- module: aws
  period: 300s
  credential_profile_name: test-mb
  metricsets:
    - ebs

5. Check Kibana dashboard or Discover for ebs data

[jsoriano]

Great!

[kaiyan-sheng]

jenkins, test this please