Fix ARN artifacts uploading/downloading

[ccressent]

Description:

With the upgrade of {download,upload}-artifact from v3 to v4, the way the release workflows gather and use the various lambda layer ARNs broke.

This changes the release workflows so that:

• each layer ARN is uploaded to a separate artifact
• those separate artifacts are downloaded and extracted together so that the rest of the pipeline works without further changes

See:

• https://github.com/actions/upload-artifact/blob/v4.6.2/README.md#not-uploading-to-the-same-artifact
• https://github.com/actions/download-artifact/blob/v4.3.0/README.md#download-multiple-filtered-artifacts-to-the-same-directory

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[amdprophet]

Looks good!