Add automated test for "Notifications System Filters Preferences"

The manual test is here: Notifications System Filters Preferences (Since XWiki 13.2 RC1)

Existing automated coverage

• NotificationsSettingsIT#notificationFiltersDefaultValues: System filters listed in user settings (rendered by the notificationsSystemFiltersPreferences macro) with their default states
• NotificationsIT#ownEventNotifications: Toggles a system filter in user settings and asserts the persisted state and its effect

Missing automated coverage

• Create a page with the notificationsSystemFiltersPreferences macro (inserted via CKEditor Insert > Other Macros)
• Assert the filters and their states match the user Notification settings
• Toggle a system filter in Notification settings; assert the page macro reflects it
• Toggle a system filter from the page macro; assert Notification settings reflect it

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/NotificationsSettingsIT.java

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