Add automated test for "User Profile Activity Stream displays all performed events"

The manual test is here: User Profile Activity Stream displays all performed events

Existing automated coverage

• NotificationsIT#displayNotificationsOnSubwikis: Events created on the main wiki and on a subwiki are both listed by a notifications macro on the main wiki (the subwiki one suffixed with "(wiki1)"). The macro has no users parameter and is on a custom page, not on the user profile.
• UsersParameterHandlerTest#handlerUsersParameter: Unit-level: the users parameter (used by the profile activity stream) is turned into a user filter.

Missing automated coverage

• Use a global user who is a member of a subwiki; log in as that user.
• Create a page on the main wiki and a page on the subwiki as that user.
• Open the user's own profile page (XWiki.<user>) and wait for the activity stream (notifications macro with users=<user>) to load.
• Assert that both creation events are listed, the subwiki one included (with its "(<wiki>)" suffix).
• Assert that events of other users are not listed there.

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/NotificationsIT.java

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