docker: add label for repo source

Author: rytswd

Dockerfile

@@ -36,8 +36,10 @@ RUN CGO_ENABLED=0 \
 # Use distroless as minimal base image to package the manager binary
 # Refer to https://github.com/GoogleContainerTools/distroless for more details
 FROM gcr.io/distroless/static:nonroot
+
+LABEL org.opencontainers.image.source = "https://github.com/numtide/multigres-operator"
 WORKDIR /
 COPY --from=builder /workspace/manager .
 USER 65532:65532
 
-ENTRYPOINT ["/manager"]
+ENTRYPOINT ["/manager"]