Add automated test for "Page Index Deleted Attachments"

The manual test is here: Page Index Deleted Attachments

Existing automated coverage

• DeletedAttachmentsIT#filterLivetableByName: Steps 2-5 for one page: attach + delete an attachment, open Deleted Attachments, filter by name and assert the deleted attachment is listed
• DeletedAttachmentsIT#filterLivetableByDate: Filtering the Deleted Attachments table by deletion date
• AllDocsIT#recycleBinTab: The Deleted attachments tab is visible to admins and hidden from guests

Missing automated coverage

• Delete attachments from both a nested (WebHome) page and a terminal page; assert all are listed in the Deleted Attachments table
• Sort by each sortable column (name, location, date, deleter) and assert the row order
• Filter by location and by deleter and assert the rows
• Click the red X (permanent delete) action for one attachment, confirm 'Yes', and assert its row disappears while the others remain
• Add a page-object method on DeletedAttachmentsPage for the permanent delete action

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/DeletedAttachmentsIT.java

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