MM-59283: Minor improvement in getClientConfig (#27825)

Overall, there is no bug here. But opportunities for
improvement.
- Used the maps.Clone function.
- Handled the error while writing to the network.

https://mattermost.atlassian.net/browse/MM-59283
```release-note
NONE
```

server/channels/api4/config.go

@@ -258,7 +258,9 @@ func getClientConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 		config = c.App.Srv().Platform().ClientConfigWithComputed()
 	}
 
-	w.Write([]byte(model.MapToJSON(config)))
+	if err := json.NewEncoder(w).Encode(config); err != nil {
+		c.Logger.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 func getEnvironmentConfig(c *Context, w http.ResponseWriter, r *http.Request) {