[DOC] Rollup explain documentation does not match product

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Looking at rollup explain documentation in https://opensearch.org/docs/latest/im-plugin/index-rollups/rollup-api/

This looks incorrect.

I created a rollup job.

[INFO] => PUT /_plugins/_rollup/jobs/books ({}) [application/json] {
  "rollup": {
    "enabled": true,
    "description": "Rollup books.",
    "schedule": {
      "interval": {
        "period": 1,
        "unit": "Minutes"
      }
    },
    "source_index": "books",
    "target_index": "books_by_order_date",
    "page_size": 1,
    "delay": 0,
    "continuous": false,
    "dimensions": [
      {
        "date_histogram": {
          "source_field": "order_date",
          "fixed_interval": "1h"
        }
      },
      {
        "terms": {
          "source_field": "title"
        }
      }
    ],
    "metrics": [
      {
        "source_field": "pages",
        "metrics": [
          {
            "sum": {}
          },
          {
            "avg": {}
          }
        ]
      }
    ]
  }
}

The explain on that job does not return this at all.

[INFO] => GET /_plugins/_rollup/jobs/books/_explain ({}) [application/json] 
[INFO] <= 200 (application/json; charset=UTF-8) | {
  "books": {
    "metadata_id": null,
    "rollup_metadata": null
  }
}

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.

2.18

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.