helm (telegraf): add {{ .Release.Namespace }} for kustomize v5.8[01] compat

### Description

* ArgoCD v3.3 has updated to [kustomize v5.8.0](https://argo-cd.readthedocs.io/en/stable/operator-manual/upgrading/3.2-3.3/#kustomize-upgraded-to-580)
* kustomize v5.8.0 has changed the way kustomize handles `helmCharts`: https://github.com/kubernetes-sigs/kustomize/pull/5940 which has a nice tl;dr:

```
TL;DR

If you use Kustomize with Helm charts, ensure that your Helm templates explicitly set the namespace, for example:

metadata:
namespace: {{ .Release.Namespace }}

If your charts already handle namespaces this way, this change should not introduce any breaking behavior.
```

Similar issues:
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### Expected Behavior

using `kustomize build --enable-helm .` renders the manifests using the proper namespaces; otherwise (when used within argocd), they might land in the default namespace (=`argocd`)

Start by locating the Telegraf chart templates that render resources and checking how they set namespaces. Run `kustomize build --enable-helm .` with the chart and verify that rendered manifests use the intended release namespace rather than the default namespace.

Written by the indexing model from the issue text.