Automatically test the "Tails documentation" link on the Desktop

The “Tails documentation” desktop launcher should open the “Documentation” page:

• in English (already tested both online & offline)
• in one language to which the website is translated
• in one language to which the website is not translated (=> English)

Feature Branch: spriver:feature/8788-automatically-test-tails-doc-shortcut

Parent Task: #10250

Related issues

• Blocked by #16976 (closed)

Original created by @intrigeri on 8788 (Redmine)