This uses skopeo to not think about docker daemons. I, however, noticed
that the docker image we had would have totally terrible cache hits, so
I rewrote it.
Fixes: https://git.lix.systems/lix-project/lix/issues/252
Change-Id: I3c5b6c1f3ba0b9dfcac212b2148f390e0cd542b7
This can release x86_64-linux binaries to staging, with ephemeral keys.
I think it's good enough to review at least at this point, so we don't
keep adding more stuff to it to make it harder to review.
Change-Id: Ie95e8f35d1252f5d014e819566f170b30eda152e
