docs: add info how to get layer versions from the SAR for the layers

[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.

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

@@            Coverage Diff            @@
##           develop      #134   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           24        24           
  Lines          706       706           
  Branches        66        67    +1     
=========================================
  Hits           706       706           

Impacted Files	Coverage Δ
aws_lambda_powertools/logging/formatter.py	100.00% <0.00%> (ø)

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[heitorlessa]

Great addition. While you're at it, could you add some quick notes on what to do after deployed?

Where can they find the Layer Arn to use? Outputs?

[heitorlessa]

Add instruction on how to find the Layern ARN after deploying the SAR App

[am29d]

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.

[am29d]

close this pr and reopened in #145 , because I screw up my fork repo and had to create new.