fix(gingress): use ENTRYPOINT instead of CMD so Kubernetes args are passed correctly

Without ENTRYPOINT, Kubernetes replaces CMD with args, causing the container
to try executing "--ingress-class=gingress" as a binary directly.

docker/gingress.Dockerfile

@@ -7,4 +7,4 @@ WORKDIR /home/appuser
 COPY ./target/release/gingress /bin
 USER appuser
 EXPOSE 80 443 8080
-CMD ["gingress"]
+ENTRYPOINT ["gingress"]