Change email address section of Add user page (#276)

Changed email address label from 'NHS email address' to 'NHS-approved
email address'.

Added text below the H1 to flag that you can only add users with an
NHS-approved email address, plus link to the list of approved domains.

<img width="437" alt="image"
src="https://github.com/user-attachments/assets/073a0ed7-2271-4c75-b561-f823a3bc1d9b"
/>

Author: Anna-Sutton

app/views/user-admin/add-user.html

@@ -45,6 +45,7 @@
       {% endif %}
 
       <h1 class="nhsuks-heading-xl">Add user</h1>
+      <p>Users must have an NHS-approved email address. See the <a href="https://digital.nhs.uk/services/care-identity-service/applications-and-services/apply-for-care-id/care-identity-email-domain-allow-list" target="_blank">list of approved email domains (opens in new tab)</a>.</p>
 
       <form action="/user-admin/check-answers" method="post" novalidate="true">
 
@@ -76,7 +77,7 @@ <h1 class="nhsuks-heading-xl">Add user</h1>
 
         {{ input({
           "label": {
-            "text": "NHS email address"
+            "text": "NHS-approved email address"
           },
           "id": "email",
           "name": "email",
@@ -95,7 +96,7 @@ <h1 class="nhsuks-heading-xl">Add user</h1>
             }
           },
           hint: {
-            text: "Only registered clinicians can assess the patient and record their consent"
+            text: "Only registered clinicians can assess the patient and record their consent."
           },
           "items": [
             {