Replace google group to GH discussions

Author: igarashitm

themes/atlasmap/layouts/partials/footer.html

@@ -18,7 +18,7 @@ <h4>Connect with us</h4>
         <a href="https://gitter.im/atlasmap/community" rel="nofollow" target="_blank" class="btn btn-primary">AtlasMap room on Gitter</a>
       </p>
       <p class="link-button">
-        <a href="https://groups.google.com/d/forum/atlasmap" rel="nofollow" target="_blank" class="btn btn-primary">AtlasMap Google Group</a>
+        <a href="https://github.com/atlasmap/atlasmap/discussions" rel="nofollow" target="_blank" class="btn btn-primary">AtlasMap Discussions</a>
       </p>
     </section>
   </div>

themes/atlasmap/layouts/partials/sidenav.html

@@ -29,7 +29,7 @@
   <li> <a href="https://docs.atlasmap.io/" target="blank"><i class='fa fa-file-text'></i> <span>User Guide</span></a> </li>
   <li> <a href="https://docs.atlasmap.io/developer-guide" target="blank"><i class='fa fa-file-text'></i> <span>Developer Guide</span></a> </li>
   <li> <a href="https://gitter.im/atlasmap/community" target="blank"><i class='fa fa-users'></i> <span>Gitter</span></a> </li>
-  <li> <a href="https://groups.google.com/g/atlasmap" target="blank"><i class='fa fa-users'></i> <span>Google Group</span></a> </li>
+  <li> <a href="https://github.com/atlasmap/atlasmap/discussions" target="blank"><i class='fa fa-users'></i> <span>Discussions</span></a> </li>
   <li> <a href="https://github.com/atlasmap/atlasmap/issues" target="blank"><i class='fa fa-life-ring'></i> <span>Report Issues</span></a> </li>
   <li> <a href="https://github.com/atlasmap/atlasmap.io/issues" target="blank"><i class='fa fa-life-ring'></i> <span>Report Website Issues</span></a> </li>
   {{ if .IsPage }}