feat: add rel="me" to Mastodon sidebar contact links for verification (#807)

This will enable verification with Mastodon by including the `rel="me"` attribute.
https://docs.joinmastodon.org/user/profile/#verification

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

_data/contact.yml

@@ -19,7 +19,7 @@
 # -
 #   type: mastodon
 #   icon: 'fab fa-mastodon'   # icons powered by <https://fontawesome.com/>
-#   url:  ''                  # Fill with your mastodon account page
+#   url:  ''                  # Fill with your Mastodon account page, rel="me" will be applied for verification
 # -
 #   type: linkedin
 #   icon: 'fab fa-linkedin'   # icons powered by <https://fontawesome.com/>

_includes/sidebar.html

@@ -81,7 +81,17 @@
 
       {% if url %}
       <a href="{{ url }}" aria-label="{{ entry.type }}"
-        {% unless entry.noblank %}target="_blank" rel="noopener"{% endunless %}>
+        {% assign link_types = nil %}
+        {% unless entry.noblank %}
+          {% assign link_types = link_types | append: " noopener" %}
+          target="_blank"
+        {% endunless %}
+
+        {% if entry.type == 'mastodon' %}
+          {% assign link_types = link_types | append: " me" %}
+        {% endif %}
+
+        {% if link_types %}rel="{{ link_types | lstrip }}"{% endif %}>
         <i class="{{ entry.icon }}"></i>
       </a>
       {% endif %}