Add S3EventNotifier example

[ptoffy]

Add S3EventNotifier example

Motivation:

There is currently no example regarding an AWS event triggered lambda, such as a lambda that gets invoked on an S3 object upload. I've had to look for a while to figure out that the AWSLambdaEvents exists and that it can be used for that (had to find out via a Java example! 😜) so I think this could be useful and a somewhat common use case

Modifications:

Added an example of a lambda that gets triggered when an object gets uploaded to an S3 bucket.

I have not described how to set up the actual S3 event in AWS because I figured if you needed such a lambda you'd know, but I can describe that too in the README if needed

[sebsto]

Thank you for your contribution. This is much appreciated. I will add some comments as a code review.
Can you also

• add this example in the CICD tool :

  swift-aws-lambda-runtime/.github/workflows/pull_request.yml

  Line 39 in bd0ec62

  examples: "[ 'APIGateway', 'APIGateway+LambdaAuthorizer', 'BackgroundTasks', 'HelloJSON', 'HelloWorld', 'ResourcesPackaging', 'S3_AWSSDK', 'S3_Soto', 'Streaming', 'Testing', 'Tutorial' ]"

• add this example in the general example readme file : https://github.com/swift-server/swift-aws-lambda-runtime/blob/main/Examples/README.md

• make sure the code pass the swift format script available at https://raw.githubusercontent.com/swiftlang/github-workflows/refs/heads/main/.github/workflows/scripts/check-swift-format.sh (beware, this tool work on staged or committed changes only. I usually run it after the git add and before git commit)

[sebsto]

Thank you for this great contribution ! I think you're on the right path. I did propose a couple of simplifications. The primary objective of the example code is readability and understandability. The code must be simple to read and understand and distraction-free.

I think there are a bit of improvement possible with this objective in mind.

I'm happy to discuss alternatives.

[ptoffy]

@sebsto I currently have no easy way to test the CLI commands you recommended, I did check them against what we have currently deployed and they look good. Should we keep them in?

[sebsto]

Thank you for the quick turnaround. I will provide additional comments on the README.
Fo the AWS CLI, I will test them before merging the PR, no worries.

The example does not compile on the CI chain.
See https://github.com/swift-server/swift-aws-lambda-runtime/actions/runs/13264375954

This is because it compiles on Linux and replacingOccurence(of:with:) is based on NSString. I guess it is not available in Foundations Essentials.

This triggers the question : did you package and deploy this code on Lambda to test it ?

[ptoffy]

Yep I have the lambda (with some additions such as the POST request) running in production just fine. I guess either AHC or some other dependency which I'm using there and we trimmed here use Foundation and it's falling back to that. I'll update this to use Foundation

[sebsto]

Thank you for all these changes. It looks good to me now. I will check the CLI command before merging

[ptoffy]

This may be unnecessary if we have the one above already? But I'm not precious about it. If you do end up leaving it, this should use block quotes too

[sebsto]

I made it on purpose - it so important and I'm sure so many will not read it :-)

[ptoffy]

I think GH markdown requires this to be in block quotes, so

> [!IMPORTANT]
> The Lambda function...

[sebsto]

You're correct - thank you