Improve definitions of previous/next relative date filters

Note: ideally this requires a site with historical config data, so that we can see the effect of filtering by relative time (previous month, current week, etc) - these tests are identical to those in MDL-72662 other than the table for reference in step 4.

1. Login as admin
2. Navigate to Reports > Config changes in site administration
3. Press Filters button
4. Using the following table as a guide, confirm you see appropriate report data after applying Filter (note this requires knowing the Current date i.e. today, so adjust Expected filter date range as you see fit):

   Current time	Filter	Expected filter
   19/01/22 09:30	Last 2 days	17/01/22 09:30 - 19/01/22 09:30
   19/01/22 09:30	Last 2 weeks	05/01/22 09:30 - 19/01/22 09:30
   19/01/22 09:30	Last 2 months	19/11/21 09:30 - 19/01/22 09:30
   19/01/22 09:30	Last 2 years	19/01/20 09:30 - 19/01/22 09:30
   19/01/22 09:30	Current day	19/01/22 00:00 - 19/01/22 23:59
   19/01/22 09:30	Current week	17/01/22 00:00 - 23/01/22 23:59
   19/01/22 09:30	Current month	01/01/22 00:00 - 31/01/22 23:59
   19/01/22 09:30	Current year	01/01/22 00:00 - 31/12/22 23:59

1. After applying the filter, only those config changes falling within Expected filter date range should be shown in the report
2. Confirm unit tests pass:

   $ vendor/bin/phpunit reportbuilder/tests/local/filters/date_test.php