feat: make post description customizable (#1602)

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Co-authored-by: Cotes Chung <11371340+cotes2020@users.noreply.github.com>

_includes/related-posts.html

@@ -81,10 +81,7 @@
               {% include datetime.html date=post.date lang=include.lang %}
               <h4 class="pt-0 my-2">{{ post.title }}</h4>
               <div class="text-muted">
-                <p>
-                  {% include no-linenos.html content=post.content %}
-                  {{ content | markdownify | strip_html | truncate: 200 | escape }}
-                </p>
+                <p>{% include post-description.html %}</p>
               </div>
             </div>
           </a>