🐛(helm) fix MinIO webhook certificate after Tilt stack changes

Restore certificate mounting for MinIO webhook communication to
backend after migrating away from unmaintained Bitnami chart.
Mount certificate in proper volume to enable secure bucket-to-backend
webhook delivery.

src/helm/extra/templates/minio.yaml

@@ -82,9 +82,15 @@ spec:
         volumeMounts:
         - mountPath: /data
           name: data
+        - mountPath: /etc/ssl/certs/mkcert-ca.pem
+          name: mkcert
+          subPath: rootCA.pem
       volumes:
       - name: data
         emptyDir:
+      - name: mkcert
+        secret:
+          secretName: mkcert
 ---
 apiVersion: batch/v1
 kind: Job