Add automated test for "Restore a deleted page"

The manual test is here: Restore a deleted page

Existing automated coverage

• DeletedDocsIT#restoreOriginalDocumentAfterDeletionAndRecreation: Page Index Deleted Pages tab restore action, but only the 'replace' variant (a page with the same name was recreated) for one page
• RecycleBinIT#restore: Restoring a deleted page from the deleted page view (not the Page Index), asserting title, content, attachment and history
• RecycleBinIT#viewDeletedPage: Deleted nested and terminal pages: restore availability per user rights from the deleted page view

Missing automated coverage

• Create a nested page (A.WebHome) and a terminal page (A.B), delete both
• Open Page Index > Deleted Pages and click 'Restore' in the Actions column for each page (no page exists at that location, so no replace modal)
• Assert each page exists again at its original reference with its original content, and is no longer listed in the Deleted Pages tab
• Add a DeletedDocsPage#restoreDoc(docName) page-object method

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

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