paperless-ngx: Enable Flower

Flower is the monitoring agent for Celery.  It has a web UI, but more
importantly, it exposes Celery performance metrics in Prometheus format.

paperless-ngx/paperless-ngx.yaml

@@ -236,9 +236,13 @@ spec:
           value: '*'
         - name: PAPERLESS_ENABLE_HTTP_REMOTE_USER
           value: '1'
+        - name: PAPERLESS_ENABLE_FLOWER
+          value: 'true'
         ports:
         - name: http
           containerPort: 8000
+        - name: flower
+          containerPort: 5555
         startupProbe:
           httpGet:
             port: 8000