[Feature Request] Add DD_SITE env var to promql-to-dd-go Helm example

[jyanadi]

Is your feature request related to a problem? Please describe.

We are trying to send Temporal metrics to DD using the example Helm Chart with ArgoCD. Since our organization is on a non-default Datadog site, the metrics are not being received by us (they are sent to the default datadoghq.com site). and the current version of the deployment.yaml does not support setting DD_SITE env var.

Describe the solution you'd like

Having the ability to set the DD_SITE env var from Helm value (dd_site) will fix the problem

env:
   - name: DD_SITE
     value: {{ .Values.dd_site }}

Additional context

The other observability examples all expose the DD_SITE env var. Only the golang solution is missing this.