chore: Integrate graphql to the express app

packages/backend/src/graphql/graphql-schema.ts

@@ -0,0 +1,9 @@
+import { buildSchema } from 'graphql';
+
+const graphQLSchema = buildSchema(`
+  type Query {
+    hello: String
+  }
+`);
+
+export default graphQLSchema;

packages/backend/src/graphql/root-resolver.ts

@@ -0,0 +1,7 @@
+const rootResolver = {
+  hello: () => {
+    return 'Hello world!';
+  },
+};
+
+export default rootResolver;