Support Elastic Agent complete wolfi image

[mrodm]

Update the Elastic Agent complete image used starting in Elastic stack versions 8.16.0-SNAPSHOT.

Follows #2038

With the logic in this PR:

• Starting with 8.16.0-SNAPSHOT, it will be used the elastic-agent-wolfi docker image: docker.elastic.co/elastic-agent/elastic-agent-wofi`
• If the test configuration specified base_image: complete:
  • Starting with 8.16.0-SNAPSHOT, it will use the complete wolfi image
  • elastic-package will use the same logic as before for older stack versions
• If the test configuration specified base_image: systemd:
  • elastic-package will use docker.elastic.co/elastic-agent/elastic-agent docker images.
  • for older stack versions it will use docker.elastic.co/beats/elastic-agent

[elasticmachine]

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• Commit: 2d62072

cc @mrodm

[rdner]

Thank you!