Fix: Docker Compose compatibility with v1 removal

[xnox]

Description

Describe your changes here:

• docker snap has shipped compose v1 & v2 for years now
• docker snap compose currently supports v1 (implied), v2, and v3 version formats of compose.yaml files
• checkbox currently used simple v1 (implied) compose.yaml files and v3 version format for the edgex compose.yaml file
• v1 compose has been deprecated upstream and will be removed
• upgrade v1 (implied) compose files to v2 format, that work with all previous docker snap revisions, and will continue to work with the future ones
• as far as i can tell, nobody uses v1 compose yaml files anymore

Resolved issues

Failing certification testing of docker snap in beta channel

Documentation

• Automated tests are included for the changed functionality in this PR. If to be merged without tests, please elaborate why.
• Necessary documentation is provided for the changed functionality in this PR (tests are documentation, too).

Tests

• Steps to follow for reviewer to run & manually test are provided.

Run docker tests against docker snap in latest/stable & latest/beta channel.

• A list of what tests were run and on what platform/configuration is provided.

Run docker tests against docker snap in latest/stable & latest/beta channel.

[yphus]

LGTM

[xnox]

@yphus

the expected result from the above is yaml file that looks like this:

version: '1'
services:
  test:
    image: ubuntu
    command: bash
    tty: true

Meaning version & services are top level keys. The error messages in the checkbox output suggest that above is producing yaml of this form

version: '2'
  services:
    test:
      ....

as if services is not a top level key.