Create nightly test for Zarf init with s3 backend

[AustinAbro321]

Describe what should be investigated or refactored

The init package is currently able to be configured with Zarf variables to support an S3 backend. See github.com/defenseunicorns/narwhal-delivery-iac-swf-reference-deployment for an example of a configuration with an s3 backend. There are no tests in this repo to ensure that this S3 backend works, so certain changes to the registry portion of the init package cannot be made with confidence.

This is the case for PR #3241 which solves a legitimate bug within the init package, but we need a test to know if this change breaks the s3 backed init package variant