Support for Vector API from Gremlin

[lvca]

Vector API are an ArcadeDB extension and not (yet) supported by Gremlin language.

We could still provide access to the vector API, like vectorNeighbors by implementing custom services.

Example of usage:

g.call('arcadedb.vectorNeighbors', [ 'indexName': 'Word[name,vector]', 'key': '<user>', 'limit': 10 ] )

[lvca]

This has been implemented. Now the return is a List<Map<Vertex,? extends Number>>. The Number is usually a float (based on configuration) that is the distance from the key. Maybe there should be a different return to be more usable in the Gremlin pipeline. I'm open to suggestions from any Gremlin expert here :-)