[AWS::BedrockAgentCore::Gateway] - [Enhancement] - rename GatewayIdentifier return value to GatewayId

### Name of the resource

Other

### Resource name

AWS::BedrockAgentCore::Gateway

### Description

As far as I have come across, AWS::BedrockAgentCore::Gateway seems to be the only resource in CloudFormation calling an ID return value "[ResourceType]**Identifier**" instead of "[ResourceType]**Id**".

See for example AWS::BedrockAgentCore::BrowserCustom, AWS::BedrockAgentCore::CodeInterpreterCustom, but also other services like AWS::EC2::Instance or AWS::APS::Workspace.

For the sake of consistency, please consider following the commonplace naming convention.

### Other Details

_No response_

Start from the issue's AWS::BedrockAgentCore::Gateway resource name and compare its GatewayIdentifier return value with the related resources named in the report. The payload names no repository files, tests, or entry points, so confirm where this CloudFormation return value is defined and how completion would be verified before beginning.

Written by the indexing model from the issue text.