Upgrade: Longhorn from 1.5.2 to 1.6.4

Change-Id: I8cdc3c0a07133f00442b496800ccc30e2c1dad61
diff --git a/charts/longhorn/templates/priorityclass.yaml b/charts/longhorn/templates/priorityclass.yaml
new file mode 100644
index 0000000..208adc8
--- /dev/null
+++ b/charts/longhorn/templates/priorityclass.yaml
@@ -0,0 +1,9 @@
+apiVersion: scheduling.k8s.io/v1
+kind: PriorityClass
+metadata:
+  name: "longhorn-critical"
+  labels: {{- include "longhorn.labels" . | nindent 4 }}
+description: "Ensure Longhorn pods have the highest priority to prevent any unexpected eviction by the Kubernetes scheduler under node pressure"
+globalDefault: false
+preemptionPolicy: PreemptLowerPriority
+value: 1000000000