Add `build_images_results.json` as an build-images workflow artifact

Motivation

With the intention of filter automatically the dispatches to do, in the https://github.com/prefapp/action-make-state-repos-dispatches, we want to upload an artifact in the build-images.yml workflow run, with the details of the images built:

Something like:

build_images_results.json

[{
        # identifier for the dispatches
    "flavor": "myflavor1",
    "image_type": "snapshots | releases",

        # version  
        # short-sha || release-tag || pre-release tag

    "image_name": "myrepo",
    "image_tag": "v1.1.0_myflavor1", 
    "repository": "foo/bar",

    "registries": [
        "myacr"
        ],

    "build_args": [ "REACT_APP_API_URL": "prod.local" ],

        # optional
    "manifest": [
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 568650436,

        "Id": "sha256:6a1341bfe7214e41ba93bd3f9fc76f392b7fa120130b6f045adc6eab1f3e3abc",
        "Created": "2021-01-18T13:43:10.642788204Z",
        ...
    ]

}]

prefapp / firestarter-workflows

Add `build_images_results.json` as an build-images workflow artifact #93

Motivation