[BUG] aggregate put_all not working with nested keys

Describe the bug
It seems that the put_all aggregate function only works with "root" keys, and do not add new nested keys.

For example, I have these 2 postfix events that I need to aggregate, based on /host/id and /email/local_id :

{
  "@timestamp": "2024-01-19T13:25:35.503436Z",
  "postfix": {
    "nrcpt": "1",
    "size": "17603"
  },
  "application": "postfix",
  "host": {
    "id": "95e0888c1df24d79a4bc827f9636cca7"
  },
  "email": {
    "from": {
      "address": "EMAIL_FROM"
    },
    "local_id": "7A20930009B"
  },
  "message": "queue active"
}

{
  "@timestamp": "2024-01-19T13:25:35.527242Z",
  "postfix": {
    "relay": "localhost[::1]:24",
    "delays": "0/0/0/0.02",
    "dsn": "2.1.5",
    "delay": "0.03",
    "status": "sent"
  },
  "application": "postfix",
  "host": {
    "id": "95e0888c1df24d79a4bc827f9636cca7"
  },
  "email": {
    "local_id": "7A20930009B",
    "to": {
      "address": "EMAIL_TO"
    }
  },
  "test": "OK"
}

The put_all function only add keys that are at the '/' level of the JSON, and drop the other keys :

{
  "@timestamp": "2024-01-19T13:25:35.503436Z",
  "postfix": {
    "nrcpt": "1",
    "size": "17603"
  },
  "application": "postfix",
  "host": {
    "id": "95e0888c1df24d79a4bc827f9636cca7"
  },
  "email": {
    "from": {
      "address": "EMAIL_FROM"
    },
    "local_id": "7A20930009B"
  },
  "message": "queue active",
  "test": "ok"
}

To Reproduce
Steps to reproduce the behavior:

pipeline:
    processor:
    - aggregate:
        identification_keys:
          - "/host/id"
          - "/email/local_id"
        action:
          put_all:
        group_duration: "10s"
        aggregate_when: '/email/local_id != null'

Expected behavior
It needs to create the missing entries in the nested keys :

{
  "@timestamp": "2024-01-19T13:25:35.503436Z",
  "postfix": {
    "nrcpt": "1",
    "size": "17603",
    "relay": "localhost[::1]:24",
    "delays": "0/0/0/0.02",
    "dsn": "2.1.5",
    "delay": "0.03",
    "status": "sent"
  },
  "application": "postfix",
  "host": {
    "id": "95e0888c1df24d79a4bc827f9636cca7"
  },
  "email": {
    "from": {
      "address": "EMAIL_FROM"
    },
    "to": {
      "address": "EMAIL_TO"
    }
    "local_id": "7A20930009B"
  },
  "message": "queue active",
  "test": "ok"
}

Environment (please complete the following information):

• latest dataprepper docker image (2.6.1)

Start by reproducing the aggregate pipeline from the issue with the two sample events and nested identification keys. Read the aggregate processor's put_all action and its existing tests, if present, to trace how nested paths are merged. Done means missing nested fields from the second event are retained in the aggregated output without breaking root-level fields.