Add basic Itinerary integration

After downloading a file, the model calls the extractor and uses the
JSON to show some basic information about the content and allows to import
the data to Itinerary. This is entirely runtime-optional; no build-time dependencies
are required and nothing changes if the extractor isn't available.

src/config-neochat.h.in

@@ -0,0 +1,8 @@
+/*
+   SPDX-FileCopyrightText: 2024 Tobias Fella <tobias.fella@kde.org>
+   SPDX-License-Identifier: LGPL-2.0-or-later
+*/
+
+#pragma once
+
+#define CMAKE_INSTALL_FULL_LIBEXECDIR_KF6 "${KDE_INSTALL_FULL_LIBEXECDIR_KF}"