[FR] crane bundle: a programmatic way of doing what docker save $(docker ps -q) does

[alexeagle]

bazel rules_docker has a JoinLayers program

https://github.com/bazelbuild/rules_docker/blob/v0.19.0/container/go/cmd/join_layers/join_layers.go

it would be nice to be able to do this with crane instead. (part of maybe-oneday having bazel rules that use only crane toolchain)