Make explain of ProjectOperator with alias show both name and alias info

[qianheng-aws]

Description

Add name information as well in the explain of ProjectOperator with alias, so user can identify whether the field in his plan comes from the right source.

POST _plugins/_sql/_explain
{
  "query": "SELECT (FlightTimeMin + 1) as FlightTimeMinPlusOne FROM opensearch_dashboards_sample_data_flights LIMIT 5"
}


#Before this PR
{
  "root": {
    "name": "ProjectOperator",
    "description": {
      "fields": "[FlightTimeMinPlusOne]"
    },
    "children": [
      {
        "name": "OpenSearchIndexScan",
        "description": {
          "request": """OpenSearchQueryRequest(indexName=opensearch_dashboards_sample_data_flights, sourceBuilder={"from":0,"size":5,"timeout":"1m","_source":{"includes":["FlightTimeMin"],"excludes":[]}}, searchDone=false)"""
        },
        "children": []
      }
    ]
  }
}

#With this PR
{
  "root": {
    "name": "ProjectOperator",
    "description": {
      "fields": "[(FlightTimeMin + 1) AS FlightTimeMinPlusOne]"
    },
    "children": [
      {
        "name": "OpenSearchIndexScan",
        "description": {
          "request": """OpenSearchQueryRequest(indexName=opensearch_dashboards_sample_data_flights, sourceBuilder={"from":0,"size":5,"timeout":"1m","_source":{"includes":["FlightTimeMin"],"excludes":[]}}, searchDone=false)"""
        },
        "children": []
      }
    ]
  }
}

Related Issues

Resolves #2901

Check List

• [x] New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] New functionality has javadoc added.
• [ ] New functionality has a user manual doc added.
• [ ] API changes companion pull request created.
• [x] Commits are signed per the DCO using --signoff.
• [ ] Public documentation issue/PR created.

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