Enable Prometheus config

[awsitcloudpro]

Issue

Issue aws#413
Issue aws#356

Description of changes

• Added ability to pass custom CloudWatch agent configuration
• Added ability to enable additional Prometheus config
• Replaced docker.io image repo by public ECR

Checklist

• Added/modified documentation as required (such as the README.md for modified charts)
• Incremented the chart version in Chart.yaml for the modified chart(s)
• Manually tested. Describe what testing was done in the testing section below
• Make sure the title of the PR is a good description that can go into the release notes

Testing

Tested by deploying the updated Helm chart in an EKS cluster.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.