Update RFC table in README (#704)

Automated changes by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub action

Author: aws-cdk-automation

FULL_INDEX.md

@@ -189,4 +189,5 @@
 [691](https://github.com/aws/aws-cdk-rfcs/issues/691)|[AWS Bedrock Integration Working Group](https://github.com/aws/aws-cdk-rfcs/issues/691)||❓unknown
 [693](https://github.com/aws/aws-cdk-rfcs/issues/693)|[Set Default Values to Construct Properties using PropertyInjector](https://github.com/aws/aws-cdk-rfcs/issues/693)||💡 proposed
 [695](https://github.com/aws/aws-cdk-rfcs/issues/695)|[AWS S3 directory bucket L2 constructs](https://github.com/aws/aws-cdk-rfcs/issues/695)||💡 proposed
+[703](https://github.com/aws/aws-cdk-rfcs/issues/703)|[apigateway: private domain name L2 construct](https://github.com/aws/aws-cdk-rfcs/issues/703)||💡 proposed
 <!--END_TABLE-->

PROPOSED.md

@@ -27,4 +27,5 @@
 [686](https://github.com/aws/aws-cdk-rfcs/issues/686)|[L2 Constructs for Bedrock](https://github.com/aws/aws-cdk-rfcs/issues/686)||💡 proposed
 [693](https://github.com/aws/aws-cdk-rfcs/issues/693)|[Set Default Values to Construct Properties using PropertyInjector](https://github.com/aws/aws-cdk-rfcs/issues/693)||💡 proposed
 [695](https://github.com/aws/aws-cdk-rfcs/issues/695)|[AWS S3 directory bucket L2 constructs](https://github.com/aws/aws-cdk-rfcs/issues/695)||💡 proposed
+[703](https://github.com/aws/aws-cdk-rfcs/issues/703)|[apigateway: private domain name L2 construct](https://github.com/aws/aws-cdk-rfcs/issues/703)||💡 proposed
 <!--END_TABLE-->