Uses deprecated `@JsonKey(ignore: true)` annotation for `copyWith` and `hashCode`

[lrsvmb]

When generating serializable classes, freezed uses the deprecated @JsonKey(ignore: true) on copyWith and hashCode. This has been deprecated since json_serializable: ^6.6.0 and I suggest updating to the most recent way : @JsonKey(includeFromJson: false, includeToJson: false)