If your objective is to store documents containing network diagrams, then it will be better to create one knowledge article for each network diagram (with a good description about the network diagram) and then attach the document containing the diagram to each knowledge article. You can use the 'Affected products' related list of knowledge articles to indicate the list of CIs which are represented in the network diagram attached to the knowledge article. Also make sure to restrict the access to these articles only to appropriate configuration management groups through user criteria.
