Add automated test for "Add exclusive filters" (Notification Tests)

The manual test is here: Add exclusive filters

Existing automated coverage

• NotificationsSettingsIT#customFiltersAndLiveData: Creates custom filters through the "Add filter" modal (location, Ignore/Notify action, "A page is modified" event type, Alert/Email format) and checks them in the custom filters Live Data. Their effect on notifications is not checked.
• NotificationsEmailsIT#notificationsEmails: Follows the entire wiki, triggers the "Notifications daily email" job and checks the received email, with no custom filter.
• ScopeNotificationFilterTest#matchPreferenceWithCorrectPreference: Unit-level matching of scope filter preferences.

Missing automated coverage

• Create pages a/b/c/d/e; user U1 has an email address, follows the entire wiki, picks the Daily email frequency and turns on the Pages alert and email toggles.
• As U1, add an Ignore filter on page c (page and children), event type "A page is modified", channel Alert.
• As U1, add an Ignore filter on page d (page and children), event type "A page is modified", channel Email.
• As another user, update pages a, b, c, d and e.
• Trigger the "Notifications daily email" scheduler job.
• Assert that U1's notification tray shows update events only for a and b.
• Assert that the email received by GreenMail lists update events only for a, b and c.

Suggested location: xwiki-platform-core/xwiki-platform-notifications/xwiki-platform-notifications-test/xwiki-platform-notifications-test-docker/src/test/it/org/xwiki/platform/notifications/test/ui/NotificationsEmailsIT.java

Found by comparing the XWiki 18.4.4 manual test runs against the automated tests on master (a0055f10a1a).