Make Gremlin operations visible for diagnostic purposes

The Gremlin client uses TCP directly, with the effect that all CosmosDB Gremlin activity is completely invisible in Application Insights. (The other storage types do better, either because AI's `HttpClient`-based dependency tracing catches it or, as with SQL Server, they have direct support for it.)

To be able to see Gremlin activity we will need to add instrumentation to the library to report activity via `Corvus.Monitoring`. (Unless Microsoft adds Application Insights support to the Gremlin client first.)