Add automated test for "Create page"

The manual test is here: Create page

Existing automated coverage

• NotificationsIT#displayNotificationsOnSubwikis: Creates a page, then displays a page holding exactly the macro call of the Dashboard activity gadget (the notifications macro with useUserPreferences=false and displayOwnEvents=true) and asserts that the created page ("Test Notif Main") is listed. The event type of the entry is not asserted.
• NotificationsIT#ownEventNotifications: A page created through the UI shows up as "created by <user>" for its creator, but in the notification tray, not in the activity stream.

Missing automated coverage

• Log in as a user and create a page through the UI.
• Go to the Dashboard (Dashboard.WebHome) and wait for its activity (notifications macro) gadget to load.
• Assert that the gadget lists an entry for the new page.
• Assert that this entry is a creation event: NotificationsContainerElement#getNotificationType is "create" and the description is "created by <user>".

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).