[BUG] There is no "output_format" in DateProcessor ingest pipeline

What is the bug?

As stated in the document: https://opensearch.org/docs/latest/ingest-pipelines/processors/date/
There should be a property for output_format on DateProcesser ingest on opensearch-java library but there is none.

How can one reproduce the bug?

use latest library from mvn:

<dependency>
    <groupId>org.opensearch.client</groupId>
    <artifactId>opensearch-java</artifactId>
    <version>2.22.0</version>
</dependency>

How can I create a pipeline like this in java?

{
  "description": "Convert date string to epoch millis",
  "processors": [
    {
      "date": {
        "field": "start_time",
        "formats": ["date_time"],
        "output_format": "epoch_millis",
        "target_field": "start_time"
      }
    }
  ]
}

What is the expected behavior?

should support output_format for the DateProcessor

Is there at least a workaround for this?

Start with the DateProcessor API in the opensearch-java 2.22.0 client and compare its supported properties with the OpenSearch date processor documentation. Reproduce the pipeline shown in the issue; done means a Java pipeline can set output_format to epoch_millis and serialize it correctly.