Refactor image pulling to use goroutines for concurrency (#1868)

## Description

Concurrently retrieves image metadata and layers during `package
create`.

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [X] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [x] Test, docs, adr added or updated as needed
- [x] [Contributor Guide
Steps](https://github.com/defenseunicorns/zarf/blob/main/CONTRIBUTING.md#developer-workflow)
followed

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Co-authored-by: razzle <[email protected]>
Co-authored-by: Wayne Starr <[email protected]>