Add query execution stats to api endpoint

[sosedoff]

New response structure would include a new field:

{
  "columns": [],
  "rows": [],
  "stats": {
    "columns_count": 3,
    "rows_count": 100,
    "rows_affected": 0,
    "query_start_time": "2022-12-25T19:06:55.893384Z",
    "query_finish_time": "2022-12-25T19:06:56.828875Z",
    "query_duration_ms": 935
  }
}