chore: add monitoring documentation (#173)

Refs: CPLP-3332
Reviewed-By:  Julia Jeroch <94133633+jjeroch@users.noreply.github.com>, Evelyn Gurschler <evelyn.gurschler@bmw.de>

developer/Technical Documentation/Architecture/operational-concept.md

@@ -27,4 +27,8 @@ Note: will be added soon
 The portal supports application and db logging. Details are stored here: https://github.com/catenax-ng/tx-portal-assets/blob/945546d91065b8870aa8f69ce94b48eac7a5ade2/docs/Technical%20Details/Auditing.md
 
 ## Monitoring
-Note: Prometheus and Grafana are planned
+Currently all backend services write log entries as structural data in json format. These logs can easily be monitored. There are several options to provide a stable monitoring solution, one of them is to setup loki and grafana. In this solution loki is used as a datasource and custom dashboards can be setup in grafana to monitor the services. Some general Properties to query with grafana are:
+
+- StatusCode - contains the status code of the response
+- Elapsed - contains the time a endpoint took to response in milliseconds
+- RenderedMessage - contains the log message with possible errors