docs: Describe the queryLogFile setting

We want to allow cluster admins to enable the query log,
however it should be noted that this is a temporary solution
for debugging situations ad-hoc and should not be enabled
permanently.

https://prometheus.io/docs/guides/query-log/

Author: philipgough

Diff for: CHANGELOG.md

@@ -1,5 +1,9 @@
 # Note: This CHANGELOG is only for the monitoring team to track all monitoring related changes. Please see OpenShift release notes for official changes.
 
+## 4.10
+
+- [#1373](https://github.com/openshift/cluster-monitoring-operator/pull/1373) Enable admins to toggle the [query_log_file](https://prometheus.io/docs/guides/query-log/#enable-the-query-log) setting for Prometheus.
+
 ## 4.9
 
 - [#1312](https://github.com/openshift/cluster-monitoring-operator/pull/1312) Support label to exclude namespaces from user-workload monitoring.

Diff for: Documentation/user-guides/configuring-cluster-monitoring.md

@@ -83,6 +83,10 @@ resources: [v1.ResourceRequirements](https://kubernetes.io/docs/api-reference/v1
 # specified by users
 externalLabels:
   [ - <labelname>: <labelvalue> ]
+# log all the queries run by the engine to a log file
+# this option should be enabled temporarily only to support debugging
+# as there is no option to support or manage log rotation
+queryLogFile: string
 ```
 
 ### AlertmanagerMainConfig

Diff for: examples/user-workload/README.md

@@ -39,4 +39,5 @@ externalLabels      map[string]string
 volumeClaimTemplate *v1.PersistentVolumeClaim
 hostport            string
 remoteWrite         []monv1.RemoteWriteSpec
+queryLogFile string
 ```