Buildkite plugin for shared SBC code

[rwadstein]

This plugin supports pushing images and params to AWS accounts and pushing ruby gems to jfrog.

There are currently 4 actions it supports: build, push_image, push_param, publish_gem.

build

No settings required except for a .buildkite/build.sh file in the repository.
If any custom functions need to be defined, define it in a .buildkite/custom_functions.sh file.

push_image

settings for environment, landscape, and account_id need to be defined in the pipeline.
For example

          - sage/sbc-shared#initial_code:
              action: push_param
              environment: production
              landscape: eu
              account_id: "700326549305"

If the qa environment you push to takes advantage of a database image used for testing, then add the env of HAS_DB_IMAGE: true

push_param

settings for environment, landscape, and account_id must be defined in the pipeline.
For example

          - sage/sbc-shared#initial_code:
              action: push_param
              environment: production
              landscape: eu
              account_id: "700326549305"

publish_gem

If the repository is used for a ruby gem, then no other settings are needed aside from the action. It does require the APP env to be passed into the container.
This only supports gem pushing via a docker container that has the gem built and assumes the docker container will execute .buildkite/releash.sh as a command.
It also had a dependency on the compose file or docker setting to mount the .buildkite folder in the container.
The reason is because the publish_gem action simply copies the release.sh script from the plugin. The docker container needs to invoke the command.
Here is an example usage:
Docker compose file

  client:
    image: s1_user_client
    environment:
      - APP
      - ART_USER
      - ART_PASS
      - CI_BRANCH
    volumes:
      - .buildkite:/usr/src/app/.buildkite

pipeline file

      - docker-compose#v3.9.0:
          run: client
          command: [".buildkite/release.sh"]
      - sage/sbc-shared#initial_code:
          action: publish_gem