Add output variables to docker action

[JeroenKnoops]

Problem

In the config you can configure docker registries and the naming of the docker images.
We want to use those names to perform additional actions on the created images like testing the image or scanning with tern

Solution

Ouput the following fields:

• image-name --> Pass image-name also as ouptut. f.e. node
• base-image --> This is the first in the list with tags. f.e. https://docker.io/philipssoftware/node:10
• all-images --> ['https://docker.io/philipssoftware/node:10', 'https://docker.io/philipssoftware/node:10.0']

Usage

- uses: philips-software/[email protected]
  id: node
  with:
    dockerfile: './docker/Dockerfile'
    image-name: 'node'
    tags: 'latest 12 12.1 12.1.4'
  env:
    DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
    DOCKER_PASSWORD: '${{ secrets.DOCKER_PASSWORD }}'
    DOCKER_ORGANIZATION: myDockerOrganization
- uses: philips-labs/[email protected]
  id: scan
  with:
    image: ${{ steps.node.outputs.base-image }}
    format: yaml
    output: ${{ steps.node.outputs.image-name }}.yaml
- uses: actions/upload-artifact@v2
  with:
    name: tern 
    path: ${{ steps.scan.outputs.file }} 

Related issues

Related to #42
42 is about showing it in the output log. This ticket is about exposing it in variables so other jobs can use it.

[JeroenKnoops]

Think about also sharing the push-branch, might be useful for expensive tasks like tern-scan to only run this on the push-branch