Add automated test for "Insert Office Document Viewer Macro"

The manual test is here: Insert Office Document Viewer Macro

Existing automated coverage

• OfficeMacroIT#viewAttachment: An office macro referencing an office attachment (page content created by the fixture) renders the document content in view mode.

Missing automated coverage

• With the office server connected and an office attachment on the page, edit the page in CKEditor and open Insert (the plus icon) > Other Macros.
• Search "Office Document Viewer", select it, fill the attachment reference and Submit.
• Save & View and assert the office document content is displayed.

Suggested location: xwiki-platform-core/xwiki-platform-office/xwiki-platform-office-test/xwiki-platform-office-test-docker/src/test/it/org/xwiki/officeimporter/test/ui/OfficeMacroIT.java

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