[monitoring-agents] Set minReplicas to 1 for VPA for VMAgent (#1894)

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## What this PR does

Set minReplicas for VPA for VMAgent to work correctly in the default
case when replicas = 1
Fixes https://github.com/cozystack/cozystack/issues/1893

### Release note

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```release-note
[monitoring-agents] set minReplicas=1 in VPA for cluster-wide VMAgent to allow recrating single replica
```

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## Summary by CodeRabbit

## Changes

* **Chores**
* Updated system monitoring autoscaler configuration to enforce minimum
replica constraints, enhancing service resilience and availability
during scaling operations.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>

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packages/system/monitoring-agents/templates/vpa.yaml

@@ -9,6 +9,7 @@ spec:
     name: vmagent
   updatePolicy:
     updateMode: Auto
+    minReplicas: 1
   resourcePolicy:
     containerPolicies:
       - containerName: config-reloader