Customized error serialization for createAsyncTask

[Yserz]

Hey,

I'm having a hard time with error mapping using reduxjs/redux-toolkit. The situation is as follows:

1. When any backend request fails it results in an error of the form:
   { message: string, code: number, label: string, }
2. When the thunk rejects the error gets serialized by miniSerializeError

   redux-toolkit/src/createAsyncThunk.ts

   Line 50 in de1282c

   export const miniSerializeError = (value: any): SerializedError => {

Result:
The label is stripped from the error.

Expected result:
createAsyncTask can be (globally) configured to keep certain attributes on errors from rejections. This could be fully optional and default to the current values.

Note when using thunkAPI.rejectWithValue:

1. The API feels to be inconsistent because the error in the action is in the payload instead of in the error attribute. There is an error in the error field though but is only including the message attribute of the error.
2. When using unwrapResult on such a value it will throw only the error from the error attribute which makes further code necessary to get the actual error from the rejected action.

IMHO it would be best to allow to specify which additional attributes on an error should be serialized when a thunk gets rejected in order to use the API in the usual way.

Related issues:
#588

[markerikson]

Fixed by #812 , I believe.