[WIP] Add support for AWS Lambda Layers to function definitions

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original description:

Add support for AWS Lambda Layers to the component so that users can specify one or more layers per Lambda function. This should include:

• Accepting a 'layers' field (list of ARNs or references) in each function's configuration.
• Adding the 'Layers' property to the AWS::Lambda::Function resources in the CloudFormation template when specified.
• Documenting the usage of Layers in the README with an example.
• Ensuring that existing functionality is not affected if 'layers' is not specified.
• Adding or updating tests to verify correct layer attachment.

Please implement this in a backwards-compatible way.

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