Fn::GetAtt intrinsic function to return the IP address of second ENI

### Name of the resource

AWS::EC2::Instance

### Resource name

_No response_

### Description

The Fn::GetAtt intrinsic function when used with the 'PrivateIp' attribute for "AWS::EC2::Instance" resource returns only the IP address associated with primary ENI currently. However, when there are multiple ENIs attached using the 'NetworkInterfaces' property, the Fn::GetAtt function cannot be used to return the IP associated with an ENI other than the primary ENI.

This is a request to add a feature such that Fn::GetAtt function can be used to return the IP associated with other ENIs.

### Other Details

_No response_

Start by reviewing the AWS::EC2::Instance Fn::GetAtt behavior for the PrivateIp attribute and how NetworkInterfaces are represented. The issue names no implementation files or tests; done means defining and validating a way for Fn::GetAtt to return the IP address associated with a non-primary ENI.

Written by the indexing model from the issue text.