docs: ec2: Add documentation to the vpcEndpointDnsEntries prop (#21701

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I mistakenly assumed this prop would contain the list of DNS names and did not realize it is actually a list of the hosted zone ID and the DNS name separated by `:`. This change includes a part of the CloudFormation documentation to the attribute to help others avoid this mistake.

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packages/@aws-cdk/aws-ec2/lib/vpc-endpoint.ts

@@ -520,6 +520,18 @@ export class InterfaceVpcEndpoint extends VpcEndpoint implements IInterfaceVpcEn
 
   /**
    * The DNS entries for the interface VPC endpoint.
+   * Each entry is a combination of the hosted zone ID and the DNS name.
+   * The entries are ordered as follows: regional public DNS, zonal public DNS, private DNS, and wildcard DNS.
+   * This order is not enforced for AWS Marketplace services.
+   *
+   * The following is an example. In the first entry, the hosted zone ID is Z1HUB23UULQXV
+   * and the DNS name is vpce-01abc23456de78f9g-12abccd3.ec2.us-east-1.vpce.amazonaws.com.
+   *
+   * ["Z1HUB23UULQXV:vpce-01abc23456de78f9g-12abccd3.ec2.us-east-1.vpce.amazonaws.com",
+   * "Z1HUB23UULQXV:vpce-01abc23456de78f9g-12abccd3-us-east-1a.ec2.us-east-1.vpce.amazonaws.com",
+   * "Z1C12344VYDITB0:ec2.us-east-1.amazonaws.com"]
+   *
+   * If you update the PrivateDnsEnabled or SubnetIds properties, the DNS entries in the list will change.
    * @attribute
    */
   public readonly vpcEndpointDnsEntries: string[];