Add a map fn for Graphqelm.Http.Error

[sporto]

Version 11 made Graphqelm.Http.Error to be different types. So something like this is not possible anymore:

type Msg 
     = MonkeyFetched (Result Grapheqlm.Http.Error  Monkey)
     | MonkeyCreated (Result Grapheqlm.Http.Error CreateMonkeyMutationResponse)

case msg of

    MonkeyFetched result ->
        case result of
            Err err ->
                ({model | monkey = Failure err})    
            ....

    MonkeyCreated result ->
        case result of
            Err err ->
                ({model | monkey = Failure err})    

In the above case it make sense to treat the fetch and creation in a similar way. Having the error being different types prevents this from compiling.

The error type needs to be homogenised first e.g.

mapGraphelmError : (a -> b) -> Graphqelm.Http.Error a -> Graphqelm.Http.Error b
mapGraphelmError fn error =
    case error of 
         Graphqelm.Http.HttpError e ->
            Graphqelm.Http.HttpError e

         Graphqelm.Http.GraphqlError parsedData errors ->
            case parsedData of
                Graphqelm.Http.GraphqlError.ParsedData parsed ->
                     Graphqelm.Http.GraphqlError (Graphqelm.Http.GraphqlError.ParsedData (fn parsed)) errors
                
                Graphqelm.Http.GraphqlError.UnparsedData v ->
                     Graphqelm.Http.GraphqlError (Graphqelm.Http.GraphqlError.UnparsedData v) errors

And then

type Msg 
     = MonkeyFetched (Result (Grapheqlm.Http.Error (Maybe Monkey)) (Maybe Monkey))
     | MonkeyCreated (Result (Grapheqlm.Http.Error CreateMonkeyMutationResponse) CreateMonkeyMutationResponse)

MonkeyCreated result ->
            case result of
                Err mutationErr ->
                    let
                        err =
                            mapGraphelmError
                                (always Nothing)
                                mutationErr
                    in
                        ( { model | data = RemoteData.Failure err }
                        , ...
                        )

So, consider adding a mapError function unless there is better solution.