Add automated test for "Create Dashboard Page with Gadgets and Columns"

The manual test is here: Create Dashboard Page with Gadgets and Columns

Existing automated coverage

• DashboardIT#editDashboard: Edits the existing Dashboard.WebHome, clicks Add Gadget, selects a gadget macro, submits and asserts the gadget count increased
• DefaultGadgetSourceTest#getGadgetWithoutScriptRight: Unit test: gadget titles using translation calls are resolved without script right (XWIKI-22817)

Missing automated coverage

• Create a nested page and a terminal page; insert the Dashboard macro via CKEditor Insert > Other Macros, Submit, Save & View
• Edit each page with the Inline form and assert the Add Gadget and Add Column buttons are present
• Add several gadgets and assert they appear
• Click Add Column and assert a new column is added
• Drag and drop gadgets into the new column, Save & View, and assert the gadget layout per column is persisted
• As a user without script right, assert the gadget titles are rendered, not displayed as code (XWIKI-22817)

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

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