Improve NXQL doc on DATE and TIMESTAMP regarding timezone

The default NXQL DATE is taken as UTC but can also be used with a time and time zone to avoid weird behavior depending on user input time zone.

For instance, if the user time zone (its browser) is set to UTC+2 and it sets a dc:expired to 2023-07-14, the date is stored as UTC 2023-07-13T22:00:00.

The following query will not match because the 2023-07-14T00:00:00 != 2023-07-13T22:00:00

SELECT * FROM Document WHERE dc:expired = DATE '2023-07-14'

The following query will not match because the 2023-07-13T00:00:00 != 2023-07-13T22:00:00

SELECT * FROM Document WHERE dc:expired = DATE '2023-07-13'

But, you can pass an explicit date with time zone or even a timestamp to have the exact match:

SELECT * FROM Note WHERE dc:expired = DATE '2023-07-13T22:00:00Z'
SELECT * FROM Note WHERE dc:expired = DATE '2023-07-14T00:00:00+02:00'
SELECT * FROM Note WHERE dc:expired = TIMESTAMP '2023-07-14T00:00:00+02:00'

Also, note that the following is working on VCS because there is a DATE cast (failing on Mongo):

SELECT * FROM Document WHERE DATE(dc:expired) = DATE '2023-07-13'