DOC-3189: Update comments callback demo

DOC-3189: Added tinycomments_fetch_author_info new option
Removes Pollyjs from old demo
added release notes for TinyMCE 7.8.0

Author: kemister85

modules/ROOT/examples/live-demos/comments-callback-with-mentions/index.html

@@ -1,4 +1,4 @@
-<textarea id="comments-callback">
+<textarea id="comments-callback-with-mentions">
 <h2>Welcome to Tiny Comments!</h2>
 <p>Please try out this demo of our Tiny Comments premium plugin with @mentions support.</p>
 <ol>

modules/ROOT/examples/live-demos/comments-callback-with-mentions/index.js

@@ -294,7 +294,7 @@ import ('https://cdn.jsdelivr.net/npm/@faker-js/faker@9/dist/index.min.js').then
 
 
   tinymce.init({
-    selector: 'textarea#comments-callback',
+    selector: 'textarea#comments-callback-with-mentions',
     license_key: 'gpl',
     toolbar: 'addcomment showcomments code | bold italic underline',
     menubar: 'file edit view insert format tools tc help',