Replace individual air-gap scripts with seactl procedure in atip-auto…

[alknopfler]

This pull request significantly updates the documentation for preparing air-gap artifacts in the atip-automated-provision.adoc file. The new instructions consolidate and simplify the process for mirroring and preloading required images and artifacts by leveraging the seactl CLI tool, replacing the previous multi-script, manual workflow. The documentation now provides clear, step-by-step guidance on using seactl for both standard and advanced scenarios, including authentication setup.

Air-gap artifact preparation and registry mirroring:

• Replaced the manual process (multiple scripts and manual image lists) for preparing and preloading air-gap artifacts with a unified workflow using the seactl CLI tool, which handles RKE2 tarball generation, Helm chart OCI mirroring, and container image mirroring in a single command.
• Added detailed instructions for creating authentication files for private registries, Rancher Apps, and SUSE Private Registry, ensuring secure and flexible registry access.
• Provided example podman commands to run the release container image with seactl mirror, covering both standard and SUSE Private Registry scenarios, and clarified how to handle output artifacts for the build process.
• Removed obsolete sections describing the old, script-based workflow and directory structure, reducing confusion and maintenance burden. (Fbf277f2L459…mated-provision