add drone docker image build

.drone.yml

@@ -0,0 +1,19 @@
+---
+# SPDX-FileCopyrightText: WTF Kooperative eG <https://wtf-eg.de/>
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+kind: pipeline
+type: docker
+name: default
+
+- name: docker-publish
+  image: plugins/docker
+  settings:
+    registry: registry.wtf-eg.net
+    repo: registry.wtf-eg.net/ki-frontend
+    target: ki-frontend
+    auto_tag: true
+    username:
+      from_secret: "docker_username"
+    password:
+      from_secret: "docker_password"