Automated backups: Add config to exclude events from triggering backups

New autobackup config (optional)

1. NB1: New config and new event helper class are well covered by unit tests.
2. NB2: This testing is a bit tricky and would require changing data directly in DB which is not really natural from user experience end. Also this is basically what the unit test does. This why this section is marked as optional.
3. NB3: This test is pretty fragile. eg I had to add tour_ended event as it was occasionally breaking the testing.
4. Set backup | backup_auto_active to Enabled.
5. Tick all days for the backup | backup_auto_weekdays setting.
6. Set backup | backup_auto_skip_modif_days to 10 days.
7. Set backup | backup_auto_skip_modif_prev to Yes.
8. Create a course.
9. Check the course id.
10. Run \core\task\automated_backup_task scheduled task. 

    php admin/cli/scheduled_task.php --execute="core\task\automated_backup_task"

11. Update mdl_backup_courses table.

    UPDATE mdl_backup_courses SET laststarttime = 1660000000, lastendtime = 1660000000, nextstarttime = 1660000000, laststatus = 1 WHERE courseid = NNN;

12. Run \core\task\automated_backup_task scheduled task one more time. 

    php admin/cli/scheduled_task.php --execute="core\task\automated_backup_task"

13. Confirm, that the course is scheduled for backup.
14. Run adhoc tasks to actually back up the course by executing . 

    php admin/cli/adhoc_task.php -e

15. Update mdl_logstore_standard_log and mdl_backup_courses tables to emulate all logs and backup happened a month ago.

    UPDATE mdl_course SET timemodified = 1650000000 WHERE id = NNN;

    UPDATE mdl_logstore_standard_log SET timecreated = 1650000000 WHERE courseid = NNN;

    UPDATE mdl_backup_courses SET laststarttime = 1660000000, lastendtime = 1660000000, nextstarttime = 1660000000, laststatus = 1 WHERE courseid = NNN;

16. Run \core\task\automated_backup_task scheduled task.
17. Confirm, that the course is skipped as not modified.
18. Reset (update) mdl_backup_courses table to emulate the backup happened a month ago.

    UPDATE mdl_backup_courses SET laststarttime = 1660000000, lastendtime = 1660000000, nextstarttime = 1660000000, laststatus = 1 WHERE courseid = NNN;

19. Create a user.
20. Enrol the user to the course.
21. Run \core\task\automated_backup_task scheduled task.
22. Confirm, that the course is scheduled for backup.
23. Reset (update) mdl_backup_courses table to emulate the backup happened a month ago.

    UPDATE mdl_backup_courses SET laststarttime = 1660000000, lastendtime = 1660000000, nextstarttime = 1660000000, laststatus = 1 WHERE courseid = NNN;

24. In backup | backup_auto_exclude_events admin setting add \tool_usertours\event\tour_ended, \core\event\role_assigned and \core\event\user_enrolment_created events events
25. Run \core\task\automated_backup_task scheduled task.
26. Confirm, that the course is skipped as not modified.
27. Reset (update) mdl_backup_courses table to emulate the backup happened a month ago.

    UPDATE mdl_backup_courses SET laststarttime = 1660000000, lastendtime = 1660000000, nextstarttime = 1660000000, laststatus = 1 WHERE courseid = NNN;

28. Access the course.
29. Navigate to question bank and cerate a true/false question.
30. Add \core\event\question_created event to backup | backup_auto_exclude_events admin setting.
31. Run \core\task\automated_backup_task scheduled task.
32. Confirm, that the course is skipped as not modified.
33. Reset (update) mdl_backup_courses table to emulate the backup happened a month ago.

    UPDATE mdl_backup_courses SET laststarttime = 1660000000, lastendtime = 1660000000, nextstarttime = 1660000000, laststatus = 1 WHERE courseid = NNN;

34. Empty backup | backup_auto_exclude_events admin setting.
35. Run \core\task\automated_backup_task scheduled task.
36. Confirm, that the course is scheduled for backup.