docs(desktop-modeler/telemetry): add variable outline events

Closes bpmn-io/variable-outline#71

Author: barinali

docs/components/modeler/desktop-modeler/telemetry/telemetry.md

@@ -212,3 +212,15 @@ Example task testing finished event:
   "incidentType": "JOB_NO_RETRIES"
 }
 ```
+
+## Variables panel events
+
+Variables panel events are sent on different interactions with the [Variables](../variables.md) panel:
+
+- User filtered variables using the search input. The search term is **not** included in the event for privacy reasons.
+- User expanded or collapsed a scope section.
+- User expanded or collapsed a variable row.
+- User copied a variable name via the copy button.
+- User copied a variable path or value via the context menu.
+
+These events do not include any additional payload data.