[BUG] Deep nested map type configuration issue in text_embedding processor

[zane-neo]

What is the bug?

When configured with deep nested map type configuration in text_embedding processor, the embedding result will override the original value of document key: pipeline configuration:

{
  "description": "An example neural search pipeline",
  "processors": [
    {
      "text_embedding": {
        "model_id": "qhO5xY4BYwgbtrHt7KDf",
        "field_map": {
          "category": {
            "name": {
              "en": "category_name_vector"
            }
          }
        }
      }
    }
  ]
}

And simulate the pipeline processor:

{
    "docs": [
        {
            "_index": "neural-search-index-v2",
            "_id": "1",
            "_source": {
                "category": [
                    {
                        "name": {
                            "en": "this is a name"
                        }
                    },
                    {
                        "name": {
                            "en": "hello world"
                        }
                    }
                ]
            }
        }
    ]
}

Result:

{
    "docs": [
        {
            "doc": {
                "_index": "neural-search-index-v2",
                "_id": "1",
                "_source": {
                    "category": [
                        {
                            "name": [
                                -0.10758455,
                                0.07971476,
                                -0.04948872,
                                ...
                            ]
                        },
                        {
                            "name": [
                                -0.034477253,
                                0.031023245,
                                0.006734962,
                                ...
                            ]
                        }
                    ]
                },
                "_ingest": {
                    "timestamp": "2024-04-10T03:51:53.496385Z"
                }
            }
        }
    ]
}

Expected result:

{
    "docs": [
        {
            "doc": {
                "_index": "neural-search-index-v2",
                "_id": "1",
                "_source": {
                    "category": [
                        {
                            "name": {
                                "category_name_vector": [
                                    -0.10758455,
                                    0.07971476,
                                    -0.04948872,
                                    ...
                                ],
                                "en": "this is a name"
                            }
                            
                        },
                        {
                            "name": {
                                "name": [
                                    -0.034477253,
                                    0.031023245,
                                    0.006734962,
                                    ...
                                ],
                                "en": "hello world"
                            }
                        }
                    ]
                },
                "_ingest": {
                    "timestamp": "2024-04-10T03:51:53.496385Z"
                }
            }
        }
    ]
}

How can one reproduce the bug?

Steps to reproduce the behavior.

What is the expected behavior?

The generated embedding results should be placed in the right position of the document.

What is your host/environment?

Operating system, version.

Do you have any screenshots?

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Do you have any additional context?

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