Add support for JanusGraph

[augustearth]

We currently support TInkerGraph and Neo4j. There is an issue with Neo4j in that the Tinkerpop - Neo4j bridge (neo4j-tinkerpop-api-impl) has not been updated since 2019. It does not seem that Neo4j is devoted to supporting Tinkerpop. As a result, the Carnival code-base is in danger of being pinned to old library versions.

JanusGraph is an Apache project that supports Tinkerpop natively. JanusGraph can employ Oracle BerkleyDB as the persistent engine, which runs in Java and should work similarly to Neo4j.

• Create a CarnivalJanus extends Carnival object.