chore(dev-cluster): raise NotificationOutbox dispatch throughput

Both central nodes ran on the NotificationOutboxOptions code defaults
(100 / 10s = 600/min) because the mounted per-node appsettings.Central.json
had no ScadaLink:NotificationOutbox section. Add the section with
DispatchBatchSize 1000 + DispatchInterval 5s — measured ~6,000/min after
restart (sweep duration becomes the binding constraint, which is fine:
the no-overlap guard self-regulates). Dev-cluster tuning only.

docker/central-node-a/appsettings.Central.json

@@ -53,6 +53,10 @@
       "AuthMode": "None",
       "FromAddress": "scada-notifications@company.com"
     },
+    "NotificationOutbox": {
+      "DispatchInterval": "00:00:05",
+      "DispatchBatchSize": 1000
+    },
     "Logging": {
       "MinimumLevel": "Information"
     }

docker/central-node-b/appsettings.Central.json

@@ -53,6 +53,10 @@
       "AuthMode": "None",
       "FromAddress": "scada-notifications@company.com"
     },
+    "NotificationOutbox": {
+      "DispatchInterval": "00:00:05",
+      "DispatchBatchSize": 1000
+    },
     "Logging": {
       "MinimumLevel": "Information"
     }