Can temporal table functions only be registered using the table API?

[Salva Alcántara]

Based on this:

https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/concepts/temporal_table_function/

It seems that the only way of registering temporal table functions is via
the Table API.

If that is the case, is there a way to make this example work

```
SELECT
  SUM(amount * rate) AS amount
FROM
  orders,
  LATERAL TABLE (rates(order_time))
WHERE
  rates.currency = orders.currency
```

without the Table API, just using SQL? E.g., is it possible to deploy the
temporal table function to the cluster (by packaging it in a jar file) and
then run the above query from the Flink SQL CLI?

Thanks in advance,

Salva