[Metricbeat] Cloudwatch metricset does not collect S3 tags correctly

[kaiyan-sheng]

• Version: master and previous branches
• Discuss Forum URL: https://discuss.elastic.co/t/aws-cloudwatch-cant-collect-s3-tags-from-aws-s3-namespace/225930
• Steps to Reproduce:

1. Make sure the AWS account you use for testing has S3 buckets(with tags).
2. Enable Metricbeat aws module: ./metricbeat modules enable aws
3. Change modules.d/aws.yml to:

- module: aws
  period: 86400s
  metricsets:
    - cloudwatch
  metrics:
    - namespace: AWS/S3
      tags.resource_type_filter: s3

4. Start Metricbeat ./metricbeat -e
5. You should see events in Kibana but no aws.tags.* field.

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)