docs: add description where to find the layer arn

[am29d]

Issue #, if available:

Description of changes:

The AWS console does not show the available versions of the SAR app for the layers we have recently published. I added the CLI command this the ARN to fetch the available versions.

I also add instruction on how to find the Layern ARN after deploying the SAR App.

Unfortunately, you have first to deploy the SAR app to get the LayerVersionArn as an exported value that can be referenced in a Lambda function resource definition. You can not do this within one SAM template and deploy the app and the lambda in one go :(.

I added two options in the documentation, either way you need to deploy two times.

Reopened PR because I screw up my fork, this was previous PR #134

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

Merging #145 into develop will not change coverage.
The diff coverage is n/a.

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  Coverage   100.00%   100.00%           
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  Files           24        24           
  Lines          706       706           
  Branches        67        67           
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  Hits           706       706           

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[heitorlessa]

Here's an example where I'm referencing the outputs of a SAR App within the same stack

https://github.com/aws-samples/aws-serverless-airline-booking/blob/develop/src/backend/payment/template.yaml

Trying to understand whether this is a new limitation OR how we built the App

[heitorlessa]

Thanks for making the changes, Alex :)

There's a minor piece in the example, since that's now using both the Layer and requirements.

It needs a more elaborate fix there, so I'll merge as-is, and we can deal with that later