Support for Solr 9

**Describe the feature:**
Add support for Solr version 9.

**Describe a specific use case for the feature:**
Enable JanusGraph to continue to function as expected with the latest version of Solr. The motivation here is primarily to ensure that we can stay up to date with vulnerability fixes as well as other security features introduced in 9.0.0.

The issue names no files, tests, or entry points. Begin by locating JanusGraph's existing Solr integration and compatibility tests, then determine the work required for Solr 9 support and verify the stated security and update goal.

Written by the indexing model from the issue text.