[BUG] Prometheus query API does not support scalar

[joshuali925]

What is the bug?
Prometheus query API does not support scalar result type

How can one reproduce the bug?
Steps to reproduce the behavior:

1. add prometheus data source
2. run query

❯ curl -X 'POST' -H 'Content-Type:application/json' --data-binary '{
  "query": "scalar(count(up))",
  "language": "PROMQL",
  "options": {
    "queryType": "instant",
    "time": "1773874502"
  }
}' --insecure -A 'kulala.nvim/5.3.4' 'localhost:9200/_plugins/_directquery/_query/my_prometheus'
{
  "status": 500,
  "error": {
    "type": "MismatchedInputException",
    "reason": "There was internal problem at backend",
    "details": "Cannot construct instance of `org.opensearch.sql.directquery.transport.model.datasource.PrometheusResult$PrometheusResultItem` (although at least one Creator exists): no int/Int-argument constructor/factory method to deserialize from Number value (1773874502)\n at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 32] (through reference chain: org.opensearch.sql.directquery.transport.model.datasource.PrometheusResult[\"result\"]-\u003ejava.util.ArrayList[0])"
  }
}%

What is the expected behavior?
should not have 500 error

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22] 87067f1
• Plugins

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Do you have any additional context?
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