add CI via woodpecker

based on docker image provided by Gadgetbridge

focus for now is getting something build. we can optimize this later and
provide our own image

.woodpecker.yml

@@ -0,0 +1,7 @@
+pipeline:
+    build:
+        image: codeberg.org/freeyourgadget/android-fdroid-tools:latest
+        commands:
+            - ./gradlew clean
+            - ./gradlew assembleConversationsFreeDebug
+            - ./gradlew assembleQuicksyFreeDebug