The current export has two problems:

- Ending time (i.e. in `created_before`) is set to the start of the day
  (00:00:00), instead of the end of the day (23:59:59). This results in
  a lot of missing events.

- If date range params are not provided, it returns the first 100,000
  events ordered by `created_at`, instead of constraining to only a
  month worth of data like in the search UI.

This change addresses the above issue and, as a result, ensures the
exported content matches with the one presented in the search UI.