[BUG] CSV reports will fail when a date field is an empty list

[zhongnansu]

Describe the bug

• Error message

{"statusCode":500,"error":"Internal Server Error","message":"Cannot read property '0' of undefined"}

For example

• mapping:

{
  "test" : {
    "mappings" : {
      "properties" : {
        "@timestamp" : {
          "type" : "date"
        },
        "dates" : {
          "type" : "date"
        },
        "message" : {
          "type" : "text",
          "fields" : {
            "keyword" : {
              "type" : "keyword",
              "ignore_above" : 256
            }
          }
        }
      }
    }
  }
}

• sample data

 {
        "_index" : "test",
        "_type" : "_doc",
        "_id" : "5",
        "_score" : 1.0,
        "_source" : {
          "@timestamp" : "2021-12-17T14:03:21",
          "message" : "first",
          "dates" : [ ]
        }
      },
      {
        "_index" : "test",
        "_type" : "_doc",
        "_id" : "4",
        "_score" : 1.0,
        "_source" : {
          "@timestamp" : "2021-12-17T14:03:21",
          "message" : "first",
          "dates" : [
            "2021-12-17T14:04:55",
            "2021-12-17T14:03:55"
          ]
        }
      },

• in Discover
  

Root cause

This code is causing the issue.
if (data._source[dateType]) will pass for an empty list, and failed the following logic. Need to put more restriction on this check. Also, for logic of parsing the only the first elements doesn't seem right. It should parse everything.

https://github.com/opensearch-project/dashboards-reports/blob/main/dashboards-reports/server/routes/utils/dataReportHelpers.ts#L117-L127

To Reproduce
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Expected behavior
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Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context
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[hlosukwakha]

Just wondering if there are any plans to address this?

Thanks