Add joined date to profiles in web UI (#16169)

app/javascript/styles/mastodon/components.scss

@@ -6769,6 +6769,17 @@ noscript {
       }
     }
 
+    .account__header__joined {
+      font-size: 14px;
+      padding: 5px 15px;
+      color: $darker-text-color;
+
+      .columns-area--mobile & {
+        padding-left: 20px;
+        padding-right: 20px;
+      }
+    }
+
     .account__header__fields {
       margin: 0;
       border-top: 1px solid lighten($ui-base-color, 12%);