🔧 Configure KI API URL from environment

With an entrypoint script, fill the configuration template from an
environment variable containing the KI API URL.

public/config.js.in

@@ -0,0 +1,7 @@
+// SPDX-FileCopyrightText: WTF Kooperative eG <https://wtf-eg.de/>
+//
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+window.ki = {
+  apiUrl: "$KI_API_URL"
+}