remove index under position property

[wrigleyDan]

Schema change that deals with the inconsistency reported in opensearch-project/user-behavior-insights#74

The schema change removes the index property under the ordinal property.

Old:

{
    ...
    "event_attributes": {
        "position": {   
            "ordinal": {
                "index": 1
            }
        }
    }
}

New:

{
    ...
    "event_attributes": {
        "position": {   
            "ordinal": 1
        }
    }
}