feat: Implement createUser mutation

packages/backend/src/graphql/mutations/create-user.ee.ts

@@ -0,0 +1,28 @@
+import User from '../../models/user';
+
+type Params = {
+  input: {
+    email: string;
+    password: string;
+  };
+};
+
+const createUser = async (_parent: unknown, params: Params) => {
+  const { email, password } = params.input;
+
+  const existingUser = await User.query().findOne({ email });
+
+  if (existingUser) {
+    throw new Error('User already exists!');
+  }
+
+  const user = await User.query().insert({
+    email,
+    password,
+    role: 'user',
+  });
+
+  return user;
+};
+
+export default createUser;