Bluesky URL prefix should not be appended (#2856)

This PR modifies

- `_config.yml` to rename `bluesky_url` into `bluesky_id`
- `_includes/social.liquid` to handle the renaming in the display of
social media icons

_includes/social.liquid

@@ -110,7 +110,7 @@
   <a href="https://facebook.com/{{ site.facebook_id }}" title="Facebook"><i class="fa-brands fa-facebook"></i></a>
 {% endif %}
 {% if site.bluesky_url %}
-  <a href="https://bsky.app/profile/{{ site.bluesky_url }}" title="Bluesky"><i class="fa-brands fa-bluesky"></i></a>
+  <a href="{{ site.bluesky_url }}" title="Bluesky"><i class="fa-brands fa-bluesky"></i></a>
 {% endif %}
 {% if site.youtube_id %}
   <a href="https://youtube.com/@{{ site.youtube_id }}" title="YouTube"><i class="fa-brands fa-youtube"></i></a>