Ability to export chats using a time range (instead of number of messages)

### Your use case

The basic chat log exporting feature implemented in https://github.com/element-hq/element-web/issues/2630 works, but I find it very limiting when you can only specify these types of ranges:
* _"Current timeline":_
It is unclear what this actually does. Like, what constitutes the beginning and end of "current"?
* _"From the beginning":_
Very rarely do you actually want to do this.
* _"Specify a number of messages":_
I never know exactly what amount of messages I want to export, because I'm not going to start counting them myself... so in practice I always end up vastly underestimating or vastly overestimating.

I would like to be able to export using a range of dates (and/or hours, depending on the situation).
Ex: from `YYYY-MM-DD HH:MM` to `YYYY-MM-DD`, or "last 6 hours", etc.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_