Add automated test for "Override a right at page level"

The manual test is here: Override a right at page level

Existing automated coverage

• UsersGroupsRightsManagementIT#allowGroupRightsAtPageLevelWhenUserRightDeniedAtWikiLevel: A right allowed at page level overrides a right denied at a higher (wiki) level, checked as the user (Edit right).
• UsersGroupsRightsManagementIT#denyUserRightAtPageLevelWhenAllowedToGroupAtPageLevel: Rights set from Administer Page > Rights: Page, checked as a newly created user.
• DefaultAuthorizationManagerIntegrationTest#inheritancePolicyForLocalWikiAccess: Integration test of right resolution: a document-level allow overrides a space-level deny.

Missing automated coverage

• Create nested pages a/b/c/d; on d, from Administer Page > Users & Rights > Rights: Page, give View only to XWikiAdminGroup
• Create terminal child page d/test and, from Edit > Access Rights on it, give View to XWikiAllGroup
• Create a new user and log in as that user
• Assert a/b/c/d is not viewable (access denied) and a/b/c/d/test is viewable

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

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