OCI-ify wrapper + packages, add docs around usage

General MR

Summary

OCI-ify the wrapper/extra package deployments. This doesn't change anything being actively used, just updates templating for wrapper/packages to support both git and OCI sources with language/defaults recommending OCI.

Also added a first-pass summary doc of how to use the wrapper/package features: https://repo1.dso.mil/big-bang/bigbang/-/blob/OCI-magicks/docs/guides/deployment-scenarios/extra-package-deployment.md

Closes #1435 (closed)