Configure `build_runner` to generate GraphQL client library

[gedenata]

It's already in step-5 and have create file build.yaml but when generate it with command

$ flutter pub run build_runner build --delete-conflicting-outputs

and look through lib/src/github_gql/ is missing some files like

├── github_oauth_credentials.dart
├── main.dart
├── src
 │   ├── github_gql
 │    │   ├── github_queries.ast.gql.dart
 │    │   ├── github_queries.graphql
 │    │   ├── github_queries.op.gql.dart
 │    │   └── github_queries.req.gql.dart
 │   └── github_login.dart
└── third_party
    └── github_graphql_schema
        ├── schema.public.ast.gql.dart
        ├── schema.public.graphql
        └── schema.public.schema.gql.dart

So, my expectation should have those file like this :