[nats] Merge container spec, not podTemplate (#1571)

## What this PR does

The NATS chart incorrectly used podTemplate+merge instead of
container+merge to add resource requests and limits to the NATS
container in the statefulset, but as a result it just completely wiped
out the default container spec. By moving the overrides under the
container key, the upstream chart now correctly merges the resource
requests, instead of overwriting the container spec.

### Release note

```release-note
[nats] Fix incorrect path to container resources in the NATS chart.
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Restructured NATS deployment configuration while maintaining existing
functionality and resource settings; templates were reorganized to
streamline how container and resource definitions are represented. No
functional or behavioral changes are expected for deployments.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/apps/nats/templates/nats.yaml

@@ -47,13 +47,9 @@ spec:
       retries: -1
   values:
     nats:
-      podTemplate:
+      container:
         merge:
-          spec:
-            containers:
-              - name: nats
-                image: nats:2.10.17-alpine
-                resources: {{- include "cozy-lib.resources.defaultingSanitize" (list .Values.resourcesPreset .Values.resources $) | nindent 22 }}
+          resources: {{- include "cozy-lib.resources.defaultingSanitize" (list .Values.resourcesPreset .Values.resources $) | nindent 12 }}
       fullnameOverride: {{ .Release.Name }}
       config:
         {{- if or (gt (len $passwords) 0) (gt (len .Values.config.merge) 0) }}