Patch policy on ImageMagick to enable PDF conversion

docker/nektar-env/Dockerfile_debian_documentation

@@ -9,4 +9,7 @@ RUN echo "deb http://deb.debian.org/debian buster non-free" > \
         apt-get install -y $(cat packages.txt) \
         && rm -rf /var/lib/apt/lists/*
 
+# Patch security policy to allow PDF conversion by ImageMagick
+RUN sed -i 's/rights="none" pattern="PDF"/rights="read|write" pattern="PDF"/g' /etc/ImageMagick-6/policy.xml
+
 USER nektar:nektar