feat: mailing to filtered teamer list

addresses #869dv9bur

templates/email/teamer_mailing.html.twig

@@ -0,0 +1,12 @@
+{% extends 'email/layout.html.twig' %}
+
+{% block body %}
+    <p>
+        {{ message | nl2br }}
+    </p>
+    <p>
+        <a href="{{ url('app_teamer_index') }}" class="button">
+            Zum Portal
+        </a>
+    </p>
+{% endblock %}