Keywords AT TIME ZONE can be followed by a column

We have queries which reference a column after `AT TIME ZONE` rather than just supplying a string. This results in a valid query which executes as expected (in PostgreSQL). The parser currently raises an error `Expected Token::SingleQuotedString after AT TIME ZONE, found: the_column`.

For example, instead of `SELECT datetime_column AT TIME ZONE 'America/Denver' FROM table` it is also valid to have `SELECT datetime_column AT TIME ZONE zone_column FROM table`

I believe further match conditions should be added here to patch: https://github.com/sqlparser-rs/sqlparser-rs/blob/main/src/parser.rs#L1322

Empieza en src/parser.rs, alrededor de la línea 1322, donde AT TIME ZONE actualmente espera una cadena entre comillas simples. Comprueba las consultas de ejemplo que usan una columna después de la palabra clave y verifica que tanto la forma literal como la forma de columna se analicen correctamente.

Escrito por el modelo de indexación a partir del texto del issue.