Date properties millisecond precision parsing changed in 7.x

[Mpdreamz]

Given the following index:

PUT /index
{
  "mappings": {
    "properties": {
      "timestamp" : {
        "type" : "date"
      }
    }
  }
}

Indexing milliseconds qualified with three digits works.

PUT /index/_doc/1
{
  "timestamp" : "2019-03-19T16:23:09.555"
}

However using two it will fail:

PUT /index/_doc/1
{
  "timestamp" : "2019-03-19T16:23:09.55"
}

{
  "error": {
    "root_cause": [
      {
        "type": "mapper_parsing_exception",
        "reason": "failed to parse field [timestamp] of type [date] in document with id '1'"
      }
    ],
    "type": "mapper_parsing_exception",
    "reason": "failed to parse field [timestamp] of type [date] in document with id '1'",
    "caused_by": {
      "type": "illegal_argument_exception",
      "reason": "failed to parse date field [2019-03-19T16:23:09.55] with format [strict_date_optional_time||epoch_millis]",
      "caused_by": {
        "type": "date_time_parse_exception",
        "reason": "Text '2019-03-19T16:23:09.55' could not be parsed, unparsed text found at index 19"
      }
    }
  },
  "status": 400
}

Specifying less then 3 digits for milliseconds worked in previous Elasticsearch versions so this is breaking change.

[elasticmachine]

Pinging @elastic/es-search