fix(dockerfile-linux): revoke the satosa user's ability to modify the entrypoint script

Guarantee the entrypoint script gets the correct permissions by
explicitly setting them at image build time.  Note that the COPY
command's `--chmod` flag requires BuildKit, which may not work in all
environments.

Author: niheconomoum

Dockerfile-linux.template

@@ -124,7 +124,8 @@ RUN set -eux; \
 VOLUME /etc/satosa
 WORKDIR /etc/satosa
 
-COPY --chown=satosa:satosa docker-entrypoint.sh /usr/local/bin/
+COPY docker-entrypoint.sh /usr/local/bin/
+RUN chmod 0755 /usr/local/bin/docker-entrypoint.sh
 ENTRYPOINT ["docker-entrypoint.sh"]
 
 EXPOSE 8080