[FIX-cloudwatch-metrics] - Use helper for serviceAccountName when using custom SA name

[mknapcok]

When making ClusterRoleBinding call helper for serviceAccountName instead of using aws-cloudwatch-metrics.fullname. In case of defining custom serviceAccount name in values file, ClusterRoleBinding is unable to use correct serviceAccount name to match to the clusterRole.

Example:
ServiceAccountName = custom-name
CLusterRoleBinding: ...
subjects:

• kind: ServiceAccount
  name: cloudwatch-metrics-aws-cloudwatch-metrics
  namespace: amazon-cloudwatch
  ...

Solution: Use same helper "aws-cloudwatch-metrics.serviceAccountName" both in creating ServiceAccount and calling it in ClusterRoleBinding

Issue

Description of changes

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

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

[ArchiFleKs]

@mknapcok Hi, thanks for the PR, need this also. Could you bump the chart version to pass the CI