Summary
Adds optional control over which version directories are copied into the aggregate site and injects a “See All Versions” option in the Documenter version selector that links to the package’s own gh-pages (or a custom URL). Useful when aggregating many repos with long version histories that might exceed Github Page's free 1 GB limit

New MultiDocRef options

• include_versions (Union{Vector{String}, Nothing}): If set (e.g. ["stable", "dev"]), only these version directories are copied from upstream; root files (e.g. index.html, versions.js) are always copied. Reduces aggregate size when many versions exist.
• all_versions_url (Union{String, Nothing}): URL for the “See All Versions” link in the version selector when include_versions is set. If unset and giturl is set, it is derived from giturl (e.g. https://github.com/org/pkg.jl.git → https://org.github.io/pkg.jl/).

Behavior
When include_versions is set:

• Version dirs are copied with follow_symlinks = true so symlinks like stable → v1.0.0 become real directories in the aggregate.
  • versions.js is rewritten so the version selector only lists the kept versions.
  • A small script is injected before </body> in each doc HTML that adds a “See All Versions” option to the version <select>. Choosing it opens the package (or custom) URL in a new tab and restores the dropdown to the current version. Only absolute http(s) URLs are used for this link.
• When include_versions is unset, behavior is unchanged (full copy, no injection).