Bump Lambdas to use Node 20 LTS instead of 18

[odevine]

As per AWS communication:

We are ending support for Node.js 18 in Lambda on September 1, 2025. This follows Node.js 18 End-Of-Life (EOL) reached on April 30, 2025 [1]. End of support does not impact function execution. Your functions will continue to run. However, they will be running on an unsupported runtime which is no longer maintained or patched by the AWS Lambda team.

• Starting on September 1, 2025, Lambda will no longer apply security patches and other updates to the Node.js 18 runtime used by Lambda functions, and functions using Node.js 18 will no longer be eligible for technical support. Also, Node.js 18 will no longer be available in the AWS Console, although you can still create and update functions using Node.js 18 via AWS CloudFormation, the AWS CLI, AWS Serverless Application Model (SAM), or other tools.
• Starting October 1, 2025, you will no longer be able to create new Lambda functions using the Node.js 18 runtime.
• Starting November 1, 2025, you will no longer be able to update existing functions using the Node.js 18 runtime.

We recommend that you upgrade your existing Node.js 18 functions to the latest available Node.js runtime in Lambda before September 1, 2025.