Release notes for Grafana 9.1.5

Alerting: Sanitize invalid label/annotation names for external alertmanagers. #54537, @JacobsonMT
Alerting: Telegram: Truncate long messages to avoid send error. #54339, @ZloyDyadka
DisplayProcessor: Handle reverse-ordered data when auto-showing millis. #54923, @leeoniya
Heatmap: Add option to reverse color scheme. #54365, @leeoniya
PluginLoader: Alias slate-react as @grafana/slate-react. #55027, @kaydelaney
Search: Add substring matcher, to bring back the old dashboard search behavior. #54813, @ArturWierzbicki
Traces: More visible span colors. #54513, @joey-grafana

Alerting: Fix incorrect propagation of org ID and other fields in rule provisioning endpoints. #54603, @alexweav
Alerting: Resetting the notification policy tree to the default policy will also restore default contact points. #54608, @alexweav
AzureMonitor: Fix custom namespaces. #54937, @asimpson
AzureMonitor: Fix issue where custom metric namespaces are not included in the metric namespace list. #54826, @andresmgot
CloudWatch: Fix display name of metric and namespace. #54860, @sunker
Cloudwatch: Fix annotation query serialization issue. #54884, @sunker
Dashboard: Fix issue where unsaved changes warning would appear even after save, and not being able to change library panels. #54706, @torkelo
Dashboard: Hide overflow content for single left pane. #54882, @lpskdl
Loki: Fix a bug where adding adhoc filters was not possible. #54920, @svennergr
Reports: Fix handling expired state. (Enterprise)