Include applicant's username in staff application emails and Discord notifications.

backend/src/main/resources/templates/staff-application-email.html

@@ -102,7 +102,7 @@
             <div>
                 <h2>Applicant</h2>
                 <ul>
-                    <li><strong>UUID:</strong> <span th:text="${application.uuid}">uuid</span></li>
+                    <li><strong>Username:</strong> <span th:text="${username}">uuid</span></li>
                     <li><strong>Email:</strong> <span th:text="${application.email}">email</span></li>
                     <li><strong>Discord:</strong> <span th:text="${application.discordUsername}">discord</span></li>
                     <li><strong>Age:</strong> <span th:text="${application.age}">age</span></li>