feat(node): add Nagios in OnPrem monitoring (#638)

* Add Nagios in OnPrem monitoring

* Update Nodes docs for Nagios in OnPrem monitoring

diagrams/onprem/monitoring.py

@@ -28,6 +28,10 @@ class Humio(_Monitoring):
     _icon = "humio.png"
 
 
+class Nagios(_Monitoring):
+    _icon = "nagios.png"
+
+
 class Newrelic(_Monitoring):
     _icon = "newrelic.png"
 

docs/nodes/onprem.md

@@ -158,6 +158,7 @@ Node classes list of onprem provider.
 - **diagrams.onprem.monitoring.Grafana**
 - **diagrams.onprem.monitoring.Humio**
 - **diagrams.onprem.monitoring.Newrelic**
+- **diagrams.onprem.monitoring.Nagios**
 - **diagrams.onprem.monitoring.PrometheusOperator**
 - **diagrams.onprem.monitoring.Prometheus**
 - **diagrams.onprem.monitoring.Sentry**