feat: Download images for a single version instead of all current versions

**What would you like to be added**: Users should be able to download and package images for a single version, e.g. `eksctl anywhere download images --version 1.24`

**Why is this needed**: The current implementation of `eksctl anywhere download images` creates a tarball containing all necessary images to create an eks-a cluster for **any** of the supported Kubernetes versions. For users working in disconnected environments that often have stricter approval and import requirements, this creates an excessively large package with many unnecessary dependencies - making the import unnecessarily difficult.

Start by locating the `eksctl anywhere download images` command and its current image-packaging flow. Trace how supported Kubernetes versions are selected, then define completion as accepting `--version 1.24` and producing a package containing only the images needed for that version.

Written by the indexing model from the issue text.