[CX] Consider duplicate fields

When parsing JSON documents with duplicate fields, e.g.

{ "name": "Bob", "name": "Joe" }

during ingestion Analytics currently rejects such documents and reports that the documents cannot be parsed. In other parts of the platform such objects are accepted, either because

• duplicate fields are removed (e.g. in the query service) or because
• there is no validation of such JSON objects.

Instead of rejecting such documents, we could consider accepting them (and possibly "correcting" them by removing additional fields) and report a warning that describes the modification.