I want this for https://github.com/bootc-dev/bootc/issues/1686
so we can distinguish pulls there.
But more generally it's can be a good idea for people writing
scripts using skopeo to set custom user agents so that registries
can more easily trace which actors are performing tasks.
Assisted-by: Claude Code
Signed-off-by: Colin Walters <walters@verbum.org>
