Added pageZoomLevel option to image renderer setup documentation (#59472)

* Added pageZoomLevel option to image renderer setup

* Update _index.md

* Update docs/sources/setup-grafana/image-rendering/_index.md

* chore: prettier run in docs

---------

Co-authored-by: Christopher Moyer <35463610+chri2547@users.noreply.github.com>

docs/sources/setup-grafana/image-rendering/_index.md

@@ -459,3 +459,19 @@ Limit the maximum device scale factor that can be requested. Default is `4`.
   }
 }
 ```
+
+#### Page zoom level
+
+The following command sets a page zoom level. The default value is `1`. A value of `1.5` equals 150% zoom.
+
+```bash
+RENDERING_VIEWPORT_PAGE_ZOOM_LEVEL=1
+```
+
+```json
+{
+  "rendering": {
+    "pageZoomLevel": 1
+  }
+}
+```