Cost Explorer API (2/n): Create terraform resources to provide credentials to the Python webserver

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For #4453, using a Cost Explorer API approach consider in #4648, create AWS IAM resources of relevance to allow for the Python webserver to make use of them via a k8s ServiceAccount. This should be very similar to #4547, but now providing Cost Explorer API permissions to the Python webserver that Grafana will work against.

Definition of done

• Terraform resources trialed to apply and be injected via a k8s ServiceAccount in the Helm deployment from Cost Explorer API (1/n): Create a Helm chart for a dummy Python webserver for use as a local support chart dependency #4670