add ability to use an image on a cache miss

[ivotron]

first of all thanks a lot for this plugin! 🙇

if I understand correctly from reading the Design section of the README, the image is built from scratch on a cache miss, is this correct? What would it take to add the ability of having a tag that can be used to reference it in the --cache-from arg for docker build in the case of cache misses? would you be open to having a PR that adds this functionality?

thanks!

[gitlon]

@ivotron

a PR seems ok, but I think you can achieve what you want with the current plugin using additional-build-args, ref README?

eg:

steps:
  - command: echo hello
    plugins:
      - seek-oss/docker-ecr-cache#v2.0.0:
          additional-build-args: '--cache-from somereg/my-image:tag'
      - docker#v3.12.0