Disable flattening of objects within the request body for the generate-all command

[yanzhudd]

Description

This PR updates the generate-all command so that only top-level objects in the request body are flattened, while all nested objects are left unflattened.

For example, The request body defined in Swagger is like this:

{
  "properties": {
    "sku": "aaa",
    "tags": "bbb",
    "properties": {
      "scheduleProfile": {
        "start": "ccc",
        "end": "ddd"
      }
    }
  }
}

After making this change, the parameter should be:

{
  "sku": "aaa",
  "tags": "bbb",
  "properties": {
    "scheduleProfile": {
      "start": "ccc",
      "end": "ddd"
    }
  }
}