Add postgres-mcp Helm chart

Wraps FreePeak/db-mcp-server: multi-database Postgres MCP driven by a
single JSON connection list, so new databases don't need a new Helm
release. Includes per-connection read_only/max_rows/query_timeout/
masking_rules guardrails and a PVC-backed audit log.

postgres-mcp/templates/pvc.yaml

@@ -0,0 +1,13 @@
+{{- if .Values.auditLog.enabled }}
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: {{ .Release.Name }}-audit-log
+spec:
+  accessModes:
+    - ReadWriteOnce
+  storageClassName: {{ .Values.auditLog.storageClass }}
+  resources:
+    requests:
+      storage: {{ .Values.auditLog.size }}
+{{- end }}