Fix issue 2489

[penghuo]

Description

• Use OpenSearch DateFieldMapper.getDefaultDateTimeFormatter as default format if format is missing.
• Remove "2015-01-01 12:10:30" related UT, the reaons is not valid OpenSearch date format.

### Create Index
PUT {{baseUrl}}/idx00003
Content-Type: application/x-ndjson

{
  "mappings": {
    "properties": {
      "timestamp": {
        "type":   "date"
      }
    }
  }
}

### Bulk index data
POST {{baseUrl}}/_bulk/
Content-Type: application/x-ndjson

{"index": {"_index": "idx00003"}}
{"timestamp": "2015-01-01 12:10:30"}

### Query Results
{

  "took": 2,
  "errors": true,
  "items": [

    {

      "index": {

        "_index": "idx00003",
        "_id": "wTtUppUBf-E1lLwjwGIJ",
        "status": 400,
        "error": {

          "type": "mapper_parsing_exception",
          "reason": "failed to parse field [timestamp] of type [date] in document with id 'wTtUppUBf-E1lLwjwGIJ'. Preview of field's value: '2015-01-01 12:10:30'",
          "caused_by": {

            "type": "illegal_argument_exception",
            "reason": "failed to parse date field [2015-01-01 12:10:30] with format [strict_date_optional_time||epoch_millis]",
            "caused_by": {

              "type": "date_time_parse_exception",
              "reason": "Failed to parse with all enclosed parsers"
            }
          }
        }
      }
    }
  ]
}

Related Issues

#2489

Check List

• 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.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.