[Gen 2][Swift][Fix doc example] Do not merge. I want to report bug on the Swift example on creating a Lambda function

Do not merge this change.

I just want to report bug on the Swift example on creating a Lambda function.

If we don't have the "authMode: AWSAuthorizationType.amazonCognitoUserPools" change, I will get the following run time error when my Swift app make the GraphQL request:

```
"Not Authorized to access sayHello on type Query"
```


Regarding the following change, ...
```
struct SayHelloResponse: Codable {
    public let sayHello: String
}

struct PushNotifyRequest {
  private static let document = 
    """
    query EchoQuery($name: String!) {
      sayHello(name: $name)
    }
    """
```
Since the "sayHello" only returns a String, a String struct doesn't have properties, such as "name" or "executionDuration". So I remove those two properties.

I only know how to fix the Swift example. I haven't fix the example for other platforms. 

Below is the document I would like to fix.
https://github.com/aws-amplify/docs/blob/main/src/pages/%5Bplatform%5D/build-a-backend/functions/set-up-function/index.mdx

Author: lightboys22

src/pages/[platform]/build-a-backend/functions/set-up-function/index.mdx

@@ -247,20 +247,12 @@ safePrint(SayHelloResponse.sayHello.name);
 
 ```swift
 struct SayHelloResponse: Codable {
-    public let sayHello: SayHello
-    
-    struct SayHello: Codable {
-        public let name: String
-        public let executionDuration: Float
-    }
+    public let sayHello: String
 }
 
 let document = """
     query EchoQuery($name: String!) {
-        sayHello(name: $name) {
-            name
-            executionDuration
-        }
+        sayHello(name: $name)
     }
     """
 
@@ -269,7 +261,8 @@ let result = try await Amplify.API.query(request: GraphQLRequest<SayHelloRespons
     variables: [
         "name": "Amplify"
     ],
-    responseType: SayHelloResponse.self
+    responseType: SayHelloResponse.self,
+    authMode: AWSAuthorizationType.amazonCognitoUserPools
 ))
 switch result {
 case .success(let response):