Skip links - use Bootstrap defaults

[stefan-korn]

Our goal is to use Bootstrap 5.3 defaults whenever possible. In case of the skip links it seems that the current solution is not utilizing Bootstrap to the full extent, especially not the recipe Bootstrap's docs are giving for skip links.

Maybe the skip links could be transformed to something like this:

    <nav class="position-absolute top-0">
      <div class="list-group visually-hidden-focusable pt-3">
        <a class="list-group-item text-nowrap" href="#header-nav">Zur Navigation</a>
        <a class="list-group-item text-nowrap" href="#header-search">Zur Suche</a>
        <a class="list-group-item text-nowrap" href="#content">Zum Inhalt</a>
      </div>
    </nav>

This way most (or ideally all) of the scss for the skip links is not needed anymore.