[Feature]: interactive sql code block

[eitsupi]

Feature Description

Thank you for working on this wonderful extension.

Since duckdb seems to work quite well, I thought it would be great if we could implement an interactive SQL code block.
It is easier to define tables (data frames) in R compared to SQL, so it would be useful to prepare data on the R side and execute the query in SQL side.

[James J Balamuta]

Hi @eitsupi, we're likely going to move to having some level of support for DBI-compliant packages that likely follows the usual Quarto approach:

```{webr-sql}
--| connection: db

SELECT * FROM "hello";
```

This is a longer-term feature.