chore(elasticloadbalancingv2): add validation for `RedirectOptions.pa…

…th` (#31202)

### Issue # (if applicable)

Closes #31201 .

### Reason for this change


If we set a string without a leading `/` for the path property, deployment will fail as shown below.

Given:

```ts
httpListener.addAction('RedirectAction', {
        conditions: [elbv2.ListenerCondition.pathPatterns(['/*'])],
        action: elbv2.ListenerAction.redirect({
          protocol: elbv2.ApplicationProtocol.HTTPS,
          path: 'example/path? ',
          permanent: true
        }),
      })
```

Result:

```sh
Failed resources:
MainStack-develop | 1:34:02 AM | CREATE_FAILED | AWS::ElasticLoadBalancingV2::ListenerRule | Alb/HttpListener/RedirectActionRule (AlbHttpListenerRedirectActionRule1D930694) Internal error reported from downstream service during operation 'The Path parameter must be a valid path, should start with a '/', and may contain up to one of each of these placeholders: '#{path}', '#{host}', '#{port}'. (Service: ElasticLoadBalancingV2, Status Code: 400, Request ID: fd4c7f01-9c97-44c1-a177-30ac04b2db26)'.
```

Related docs: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-elasticloadbalancingv2-listenerrule-redirectconfig.html#cfn-elasticloadbalancingv2-listenerrule-redirectconfig-path

### Description of changes

Add validation for `path` prop like below.

```ts
    if (options.path && !options.path.startsWith('/')) {
      throw new Error('Redirect path must start with a \'/\'');
    }
```

### Description of how you validated changes

Add unit test.

### 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*

packages/aws-cdk-lib/aws-elasticloadbalancingv2/README.md

@@ -193,6 +193,8 @@ If you do not provide any options for this method, it redirects HTTP port 80 to
 By default all ingress traffic will be allowed on the source port. If you want to be more selective with your
 ingress rules then set `open: false` and use the listener's `connections` object to selectively grant access to the listener.
 
+**Note**: The `path` parameter must start with a `/`.
+
 ### Application Load Balancer attributes
 
 You can modify attributes of Application Load Balancers:

packages/aws-cdk-lib/aws-elasticloadbalancingv2/lib/alb/application-listener-action.ts

@@ -2,7 +2,7 @@ import { Construct, IConstruct } from 'constructs';
 import { IApplicationListener } from './application-listener';
 import { IApplicationTargetGroup } from './application-target-group';
 import { Port } from '../../../aws-ec2';
-import { Duration, SecretValue, Tokenization } from '../../../core';
+import { Duration, SecretValue, Token, Tokenization } from '../../../core';
 import { CfnListener, CfnListenerRule } from '../elasticloadbalancingv2.generated';
 import { IListenerAction } from '../shared/listener-action';
 
@@ -115,6 +115,9 @@ export class ListenerAction implements IListenerAction {
     if ([options.host, options.path, options.port, options.protocol, options.query].findIndex(x => x !== undefined) === -1) {
       throw new Error('To prevent redirect loops, set at least one of \'protocol\', \'host\', \'port\', \'path\', or \'query\'.');
     }
+    if (options.path && !Token.isUnresolved(options.path) && !options.path.startsWith('/')) {
+      throw new Error(`Redirect path must start with a \'/\', got: ${options.path}`);
+    }
 
     return new ListenerAction({
       type: 'redirect',

packages/aws-cdk-lib/aws-elasticloadbalancingv2/test/alb/actions.test.ts

@@ -338,4 +338,19 @@ describe('tests', () => {
       ],
     });
   });
+
+  test('throw error for invalid path pattern for redirect action', () => {
+    // GIVEN
+    const listener = lb.addListener('Listener', { port: 80 });
+
+    // THEN
+    expect(() => {
+      listener.addAction('RedirectAction', {
+        action: elbv2.ListenerAction.redirect({
+          protocol: elbv2.ApplicationProtocol.HTTPS,
+          path: 'example',
+        }),
+      });
+    }).toThrow('Redirect path must start with a \'/\', got: example');
+  });
 });