[Bug] Grafana Plugin - variables not accepted in SQL "Drop Down List" query editor

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Version

IoTDB v1.3.2 in docker on MacOS

### Describe the bug and provide the minimal reproduce step

A variable for a device path has been created as per instructions.
This variable can be used successfully in the "SQL Full-Customized" query editor

As per the excellent documentation [1]

> Both SQL: Full Customized and *SQL: Drop-down List* input methods support the variable and template functions of grafana

However, trying to add the sensor path at the dropdown element shown as `"$endpoint"` below ...

[root] > [dropdown-sg] > "$endpoint"

... I get the following error:

> $endpoint is illegal, unquoted node name can only consist of digits, characters and underscore, or start or end with wildcard

Note: I have tried `$endpoint` `${endpoint}` and `{{endpoint}}` form of variable template syntax.

[1]: https://iotdb.apache.org/UserGuide/latest/Ecosystem-Integration/Grafana-Plugin.html#create-a-new-panel

### What did you expect to see?

Variable template syntax shown in path element instead of regular path component from dropdown

### What did you see instead?

Error

### Anything else?

I notice the source repo for the grafana plugin (iotdb-extras) does not have any issues tracked. I can re-submit there if required.

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Inizia riproducendo il problema nell’editor SQL Drop-down List del plugin Grafana con IoTDB v1.3.2, confrontandolo con l’editor SQL Full-Customized. Esamina quindi il codice sorgente del plugin in iotdb-extras e la documentazione collegata del plugin Grafana. Il lavoro è completato quando una variabile del percorso del dispositivo viene accettata nell’editor a discesa invece di essere analizzata come un nodo di percorso letterale illegale.

Scritto dal modello di indicizzazione a partire dal testo della issue.