Inheritable JsonKey with Freezed

This issue is related to https://github.com/rrousselGit/freezed/issues/423

**Is your feature request related to a problem? Please describe.**
I'm building an API wrapper, and I'm dealing with two JSON object that have numerous shared keys and only a few specific ones. I have an interface like this to implement this:

```dart
abstract class MyBaseType {
@JsonKey(name: 'property_key')
final String property;
}
```

And a couple of freezed classes like this:

```dart
@freezed
class MySpecializedType extends MyBaseType with _$MySpecializedType {
const MySpecializedType._();

const factory MySpecializedType({
required String property,
@JsonKey(name: 'another_propery_key') required String anotherProperty,
}) = _MySpecializedType
}
```

Normally, when using json_serializable, the JsonKey annotation in the base class will be used in subclasses. This is not happening when using freezed.

**Describe the solution you'd like**
I'd like JsonKey annotations used in superclasses to be used in freezed subclasses as well.

**Describe alternatives you've considered**
The only alternative is writing the same annotation everywhere it's needed.