Fix: Add preStop hook to allow graceful network shutdown (#121)

Adding a preStop sleep to allow other controllers to remove the pod from the network path.
Without, there's a risk of breaking in-flight requests when the container is already stopped but the endpoints/endpointsSlice objects haven't been updated.

Source:  https://learnk8s.io/graceful-shutdown

charts/qdrant/templates/statefulset.yaml

@@ -157,6 +157,10 @@ spec:
           securityContext:
             {{- toYaml . | nindent 12 }}
           {{- end }}
+          lifecycle:
+            preStop:
+              exec:
+                command: ["sleep", "3"]
           volumeMounts:
           - name: qdrant-storage
             mountPath: /qdrant/storage