Add sql.boolean to query builder

please reopen #711 


>  ```ts
> sql.fragment`${true}`
> ```
> 
> becomes a postgres text
> 
> ```ts
> sql.fragment`true`
> ```
> 
> becomes a postgres bool
> 
> I need the postgres boolean... which is why I'd prefer
> 
> ```ts
> sql.fragment`sql.boolean(true)`
> ```
