add option to consider the exact hour when comparing timestamps to today

This is a feature request, but the feature request issue template required a lot of fields that are not needed so I used the blank template.

org-agenda has some variables to ignore items with timestamps in the future, like `org-agenda-todo-ignore-timestamp` when the value is 'future. That can be easily done in org-ql with the predicate `(ts-active :to 'today)`. In both cases, the exact hour and minutes are not considered, and only the date is compared. But in the case of org-agenda, the variable `org-agenda-todo-ignore-time-comparison-use-seconds` allows to compare timestamps down to the second, so that for example items scheduled today but at a later hour are not shown. I think it would be nice to have something like that in org-ql too.

A good solution could be to allow also to use the value 'now in those predicates. Introducing that is trivial and I did so in my fork: https://github.com/igmacs/org-ql/commit/dec2377cb6a5fe5fbb03ca80fb2ae986a39458fa. If you like it, I can document it and make a PR