Update cloudwatch-metrics chart to allow env vars to passed in

[charlierm]

Issue

Description of changes

This adds the ability to pass in additional environment variables into the cloudwatch-agent daemonset. This is particuarly useful for using RUN_WITH_IRSA.

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

I ran this locally, testing different environment variables, bools, strings and numbers all seem to work as expected.

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