I’m researching using Apache Solr with WordPress and I wanted to see if WP Solr could help with my client’s specific requirements. They will have one main WP site where users will be doing the searching, but they also have ~5 other sites that are not WP that need to be included in the index and have results returned when a user searches on the main site. Is this possible with WP Solr and Apache Solr? I was thinking of using OpenSolr as the hosting provider. If this is possible, can you explain the setup that I would need to make this work?