[utils] Fix define_var in ajax context (closes #4881301)
Use namespaced <cubicweb:script> instead of just <script>
#! /bin/sh -e#if [ "$1" = configure ]; then if which install-docs >/dev/null 2>&1; then install-docs -i /usr/share/doc-base/cubicweb-doc fifi#DEBHELPER#exit 0