Add label org.opencontainers.image.source

Closes #5191

Dockerfile

@@ -1,7 +1,8 @@
 FROM --platform=linux/amd64 ubuntu:23.10 as wekan
 LABEL maintainer="wekan" \
       org.opencontainers.image.ref.name="ubuntu" \
-      org.opencontainers.image.version="23.10"
+      org.opencontainers.image.version="23.10" \
+      org.opencontainers.image.source="https://github.com/wekan/wekan"
 
 # 2022-09-04:
 # - above "--platform=linux/amd64 ubuntu:22.04 as wekan" is needed to build Dockerfile