feat(apigatewayv2): support for setting routeSelectionExpression for an HTTP API (#31373)

### Issue # (if applicable)

Closes #31104.

### Reason for this change

Cloudformation supports for configuring `routeSelectionExpression` but AWS CDK doesn't support this.

### Description of changes

Added `routeSelectionExpression` prop to `HttpApiProps`.

For HTTP API, `routeSelectionExpression` must be `${request.method} ${request.path}`. Therefore, I defined `routeSelectionExpression` as boolean and set it to `${request.method} ${request.path}`.

### Description of how you validated changes

Added unit and integ tests.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: badmintoncryer

packages/@aws-cdk-testing/framework-integ/test/aws-apigatewayv2/test/http/integ.api.js.snapshot/aws-cdk-aws-apigatewayv2.assets.json

@@ -4,7 +4,8 @@
    "Type": "AWS::ApiGatewayV2::Api",
    "Properties": {
     "Name": "HttpApi",
-    "ProtocolType": "HTTP"
+    "ProtocolType": "HTTP",
+    "RouteSelectionExpression": "${request.method} ${request.path}"
    }
   },
   "HttpApiDefaultStage3EEB07D6": {

packages/@aws-cdk-testing/framework-integ/test/aws-apigatewayv2/test/http/integ.api.js.snapshot/aws-cdk-aws-apigatewayv2.template.json

@@ -6,7 +6,9 @@ import * as apigw from 'aws-cdk-lib/aws-apigatewayv2';
 const app = new cdk.App();
 const stack = new cdk.Stack(app, 'aws-cdk-aws-apigatewayv2');
 
-new apigw.HttpApi(stack, 'HttpApi');
+new apigw.HttpApi(stack, 'HttpApi', {
+  routeSelectionExpression: true,
+});
 
 new IntegTest(app, 'http-api', {
   testCases: [stack],

packages/@aws-cdk-testing/framework-integ/test/aws-apigatewayv2/test/http/integ.api.js.snapshot/cdk.out

@@ -93,6 +93,14 @@ new apigwv2.HttpApi(this, 'HttpProxyApi', {
 });
 ```
 
+The `routeSelectionExpression` option allows configuring the HTTP API to accept only `${request.method} ${request.path}`. Setting it to `true` automatically applies this value.
+
+```ts
+new apigwv2.HttpApi(this, 'HttpProxyApi', {
+  routeSelectionExpression: true,
+});
+```
+
 ### Cross Origin Resource Sharing (CORS)
 
 [Cross-origin resource sharing (CORS)](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS) is a browser security

packages/@aws-cdk-testing/framework-integ/test/aws-apigatewayv2/test/http/integ.api.js.snapshot/httpapiDefaultTestDeployAssert77633A40.assets.json

@@ -160,6 +160,15 @@ export interface HttpApiProps {
    * @default - no default authorization scopes
    */
   readonly defaultAuthorizationScopes?: string[];
+
+  /**
+   * Whether to set the default route selection expression for the API.
+   *
+   * When enabled, "${request.method} ${request.path}" is set as the default route selection expression.
+   *
+   * @default false
+   */
+  readonly routeSelectionExpression?: boolean;
 }
 
 /**
@@ -434,6 +443,7 @@ export class HttpApi extends HttpApiBase {
       corsConfiguration,
       description: props?.description,
       disableExecuteApiEndpoint: this.disableExecuteApiEndpoint,
+      routeSelectionExpression: props?.routeSelectionExpression ? '${request.method} ${request.path}' : undefined,
     };
 
     const resource = new CfnApi(this, 'Resource', apiProps);