Add run-image option

[jquick]

One final addition!

We have ran into this case a few times where one of the following happens:

• A image was created outside of the docker-compose-plugin but we still want to execute run commands on it
  • This is usually from a manual docker build
• Multiple images were created (with different names) for a single service. In this case the plugin will always pull the latest one created
  • This is usually from separate architecture builds which we combine later but want to test individually

For these cases we can inject an:

buildkite-agent meta-data set docker-compose-plugin-built-image-tag*

before running but I think an official option would be helpful.

This PR adds a new run-image option where you can pass an image and it will try to run with it.

An example:

  - label: ":docker: Build (multiplatform)"
    command: >-
      docker buildx build
      --target build
      --platform "linux/amd64,linux/arm64"
      --build-arg BUILDKIT_INLINE_CACHE=1
      --cache-from "${DOCKER_BUILD_BASE}/example/build:unstable-multi"
      -t "${DOCKER_BUILD_BASE}/example/build:${CI_BUILD_ID}"
      example/ 

  - label: ":golang: Test"
    command: go test -v ./...
    plugins:
      - ${DOCKER_COMPOSE_PLUGIN}:
          run: build
          run-image: ${DOCKER_BUILD_BASE}/example/build:${CI_BUILD_ID}

[jquick]

Thanks @toote! I updated with your suggestions and it looks good!

Did some testing with and without the override and I am happy with the results. Appreciate the feedback and guidance!