needs.json: warn if key and `id` field differs

[ubmarco]

Sphinx-Needs allows to import this needs.json:

{
  "current_version": "1.0",
  "project": "test project",
  "versions": {
    "1.0": {
      "creator": { "program": "sphinx_needs", "version": "4.2.0" },
      "needs": {
        "REQ_1_1": {
          "id": "REQ_1_1_other",
          "other": "fields"
        }
      },
      "needs_amount": 1,
      "needs_schema": {
        "$schema": "[http://json-schema.org/draft-07/schema#](http://json-schema.org/draft-07/schema)",
        "properties": {
          "fields": {}
        },
        "type": "object"
      }
    }
  }
}

The dictionary key REQ_1_1 differs from the id field value REQ_1_1_other.
This should lead to a warning and a refusal to import those needs.