chore(cx-api): only include v1 feature flags in the Flags with a different default in v2 section (#32766)

### Issue # (if applicable)

Closes #<issue number here>.

### Reason for this change

The docs listing feature flags in v1 with a different default in v2 currently includes some feature flags that were introduced in v2: https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/cx-api/FEATURE_FLAGS.md#flags-with-a-different-default-in-v2 . 

### Description of changes

Update the filter to check if the feature flag was introduced in v1 to avoid accidentally including v2 feature flags with default 
`true`.

### Describe any new or updated permissions being added

N/A

### Description of how you validated changes

ran `yarn build` to update `FEATURE_FLAGS.md` 

### 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: gracelu0

packages/aws-cdk-lib/cx-api/FEATURE_FLAGS.md

@@ -219,10 +219,7 @@ Here is an example of a `cdk.json` file that restores v1 behavior for these flag
     "@aws-cdk/aws-rds:lowercaseDbIdentifier": false,
     "@aws-cdk/aws-apigateway:usagePlanKeyOrderInsensitiveId": false,
     "@aws-cdk/aws-lambda:recognizeVersionProps": false,
-    "@aws-cdk/aws-cloudfront:defaultSecurityPolicyTLSv1.2_2021": false,
-    "@aws-cdk/pipelines:reduceAssetRoleTrustScope": false,
-    "@aws-cdk/aws-stepfunctions-tasks:useNewS3UriParametersForBedrockInvokeModelTask": false,
-    "@aws-cdk/core:aspectStabilization": false
+    "@aws-cdk/aws-cloudfront:defaultSecurityPolicyTLSv1.2_2021": false
   }
 }
 ```

packages/aws-cdk-lib/cx-api/build-tools/flag-report.ts

@@ -65,7 +65,7 @@ function changedFlags() {
 }
 
 function migrateJson() {
-  const changedInV2 = flags(flag => !!flag.defaults?.v2 && !!flag.introducedIn.v2);
+  const changedInV2 = flags(flag => !!flag.defaults?.v2 && !!flag.introducedIn.v2 && !!flag.introducedIn.v1);
 
   const context = Object.fromEntries(changedInV2.map(([name, _]) => [name, false]));