Support AT TIME ZONE clause

[tinfoil-knight]

Which issue does this PR close?

Closes #9580 .

Rationale for this change

AT TIME ZONE clause wasn't supported by DataFusion. For eg:

SELECT '2000-12-01 04:04:12' AT TIME ZONE 'America/New_York');

would earlier lead to this error: This feature is not implemented: Unsupported ast node in sqltorel: AtTimeZone

Now, the query evaluates to:

+-----------------------------+
| Utf8("2000-12-01 04:04:12") |
+-----------------------------+
| 2000-12-01T04:04:12-05:00   |
+-----------------------------+

What changes are included in this PR?

This PR adds support for converting AtTimeZone expression provided by sqlparser-rs to a logical expression in DataFusion.

Are these changes tested?

Yes. New tests have been added for expected behaviour and error scenarios.

Are there any user-facing changes?

Yes. The addition of AT TIME ZONE clause is a user facing change.

No breaking change since this PR only adds support for a previously unsupported clause.

[alamb]

Looks good to me -- thank you @tinfoil-knight