mergeV with onMerge when extra properties are unknown

jobId = "spark:bdx_job_1"

// Initial vertices
vertices = [
    [
        (T.id): "spark:bdx_job_1",
        (T.label): "job",
        "url": single("spark://some/url"),
        "status": single("running"),
    ],
]

// First insertion
g.inject(vertices) \
    .unfold() \
    .mergeV() \
    .iterate()

// Updated vertices
updatedVertices = vertices = [
    [
        (T.id): jobId,
        (T.label): "job",
        "url": "spark://another/url",
        "status": "completed"
        }
    ]
]