library/roles/ckan/ckan/defaults/main.yml: add xmltodict to the pip modules.

d4science-ghn-cluster/group_vars/ckan_prod/ckan_prod.yml: Install the ckan-dcat module in production.

ckan/ckan/defaults/main.yml

@@ -110,6 +110,7 @@ ckan_pip_dependencies:
   - cryptography
   - idna
   - certifi
+  - xmltodict
 
 ckan_pip_versioned_dependencies:
   - { name: 'SQLAlchemy', version: '0.9.6', state: 'present' }