chore(codepipeline): generate stack name in codepipeline when stack name is unresolved token (#31967)

### Issue # (if applicable)

Closes #31436.

### Reason for this change

When nested stack is used with CodePipeline, the stack name is actually a token which will fail regex check. We can't simply add a `Token.isUnresolved` check before the regex check because stack name must be a resolved string otherwise the template file would include `Token[xxx]`.


### Description of changes

The only feasible fix would be allowing users to override the nested stack name if users provide one. Currently nested stack names are auto-generated and are a token value. Allow users to specify the stack name.

### Description of how you validated changes

New integ tests pass. Existing tests pass.

### Checklist
- [ ] 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: GavinZZ

packages/@aws-cdk-testing/framework-integ/test/aws-codepipeline-actions/test/integ.codepipeline-with-nested-stack.js.snapshot/cdk.out

@@ -0,0 +1,57 @@
+{
+ "Resources": {
+  "PipelineCrossRegionStackNestedStackPipelineCrossRegionStackNestedStackResourceAABDCA01": {
+   "Type": "AWS::CloudFormation::Stack",
+   "Properties": {
+    "TemplateURL": {
+     "Fn::Join": [
+      "",
+      [
+       "https://s3.us-east-1.",
+       {
+        "Ref": "AWS::URLSuffix"
+       },
+       "/cdk-hnb659fds-assets-123456789012-us-east-1/e9bdb2e29c996292dd4a35bf37486dfd5d453c102ecee8dd47db844ba97465d6.json"
+      ]
+     ]
+    }
+   },
+   "UpdateReplacePolicy": "Delete",
+   "DeletionPolicy": "Delete"
+  }
+ },
+ "Parameters": {
+  "BootstrapVersion": {
+   "Type": "AWS::SSM::Parameter::Value<String>",
+   "Default": "/cdk-bootstrap/hnb659fds/version",
+   "Description": "Version of the CDK Bootstrap resources in this environment, automatically retrieved from SSM Parameter Store. [cdk:skip]"
+  }
+ },
+ "Rules": {
+  "CheckBootstrapVersion": {
+   "Assertions": [
+    {
+     "Assert": {
+      "Fn::Not": [
+       {
+        "Fn::Contains": [
+         [
+          "1",
+          "2",
+          "3",
+          "4",
+          "5"
+         ],
+         {
+          "Ref": "BootstrapVersion"
+         }
+        ]
+       }
+      ]
+     },
+     "AssertDescription": "CDK bootstrap stack version 6 required. Please run 'cdk bootstrap' with a recent version of the CDK CLI."
+    }
+   ]
+  }
+ }
+}