Enhance DiscordAppeal submission process by adding username retrieval and updating email notifications with Minecraft username. Refactor for clarity and consistency in variable usage.

backend/src/main/resources/templates/discord-appeal-email.html

@@ -102,8 +102,9 @@
                 <div>
                     <h2>User information</h2>
                     <ul>
-                        <li><strong>Username:</strong> <span th:text="${appeal.discordUsername}">username</span></li>
+                        <li><strong>Discord Username:</strong> <span th:text="${appeal.discordUsername}">dc username</span></li>
                         <li><strong>UUID:</strong> <span th:text="${appeal.uuid}">uuid</span></li>
+                        <li><strong>Minecraft Username:</strong> <span th:text="${minecraftName}">mc username</span></li>
                         <li><strong>Email:</strong> <span th:text="${appeal.email}">email</span></li>
                         <li><strong>Submitted at:</strong> <span th:text="${createdAt}">date</span></li>
                     </ul>