feat(ShowEnvelope): render envelope message using Markdown parser

EnvelopeGenerator.Web/Views/Envelope/ShowEnvelope.cshtml

@@ -79,7 +79,7 @@
                 }
                 else
                 {
-                <h6>@($"{@envelope?.Message}")</h6>
+                <div id="envelope-message"></div>
                 }
                 <p>
                     <small class="text-body-secondary">
@@ -134,6 +134,8 @@
 @if (!isReadOnly)
 {
 <script nonce="@nonce">
+    document.getElementById('envelope-message').innerHTML = marked.parse('@(envelope?.Message)');
+
     document.getElementById('readonly-send').addEventListener('click', async () => {
         const receiverMail = document.getElementById('readonly-receiver-mail');
         const dateValid = document.getElementById('readonly-date-valid');