docs: add docs for LogPanel

docs/user/widgets/log_panel/log_panel.md

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+(user.widgets.log_panel)=
+
+# LogPanel widget
+
+The LogPanel widget can be used to view logs:
+
+![LogPanel](./logpanel.png)
+
+It automatically subscribes to log updates. You can fetch the log history with the "Fetch history" button.
+
+## Filtering based on log level
+
+If you select a dropdown box, only logs of that priority level or higher will be displayed:
+
+![LogPanel](./logpanel_level.png)
+
+
+## Filtering based on a search string
+
+If you type in a search string into the box in the toolbar, and hit enter or press the update button, that filter will be applied:
+
+![LogPanel](./logpanel_text.png)
+
+This search uses the [Python regular expression syntax](https://docs.python.org/3/library/re.html) if the checkbox for this option is selected:
+
+![LogPanel](./logpanel_regex.png)
+
+
+## Filtering based on time range
+
+You may filter the logs to those occurring within a given time range.
+
+![LogPanel](./logpanel_timerange.png)
+
+## Filtering based on service
+
+You can select which services to show logs from.
+
+![LogPanel](./logpanel_services.png)