Now that we have ES at a modern version, we should consider bringing Solr to a modern version as well.
The focus of this work would be to get us in a place where Solr is upgraded, along with the related work of building out the Solr functionality to parity with Elasticsearch. The goal would not be to add net new functionality, just to get Solr and ES in the same place for the alerts UI and REST interface. Additionally, it would include the various supporting necessities such as ensuring associated DAOs are testable, and so on. Given the testing, reviewing, and iteration involved, I'd like to propose doing this work in a feature in a feature branch. Jiras would be created based on this discussion once it dies down a bit.
