feat: added data based dynamic navigation for site header

src/_data/navigation.json

@@ -0,0 +1,12 @@
+{
+  "items": [
+    {
+	"text": "Start",
+	"url": "/"
+    },
+    {
+      "text": "Kontakt",
+      "url": "/contact/"
+    }
+  ]
+}

src/_includes/partials/site-head.html

@@ -11,8 +11,10 @@ SPDX-License-Identifier: GPL-3.0-or-later
       </button>
       <div class="collapse navbar-collapse" id="navbarCollapse">
 	<div class="navbar-nav">
-	  <a href="/" class="nav-item nav-link active">Start</a>
-	  <a href="/contact" class="nav-item nav-link active">Kontakt</a>
+	  {% for item in navigation.items %}
+	  <a href="{{ item.url }}" class="nav-item nav-link active">
+	    {{ item.text }}</a>
+	  {% endfor %}
 	</div>
   </nav>
 </header>