Add an example of product name not known (#400)

We do not always get a product name as part of the vaccination history
(as it may not have been recorded).

In these scenarios, we’ve decided to show "Not known" in the secondary
text colour (dark grey) rather than leave it blank. This is clearer and
resolves a potential accessibility issue.

<img width="1020" height="469" alt="Screenshot 2025-07-15 at 18 14 10"
src="https://github.com/user-attachments/assets/746314e2-8a06-4cdd-a8d3-06964e6c5d08"
/>

Author: frankieroberto

app/views/record-vaccinations/patient-history.html

@@ -166,7 +166,8 @@ <h2 class="nhsuk-heading-m">Vaccination history</h2>
                 text: "Flu"
               },
               {
-                text: "Adjuvanted Quadrivalent Influenza Vaccine (aQIV)"
+                text: "Not known",
+                classes: "nhsuk-u-secondary-text-color"
               }
             ],
             [