docker_push: allow passing cred_helpers from toolchain into commands

[manuelnaranjo]

When an environment sets up the credentials helpers and configuration it's expected the behaviour that container_pull provides is also offered by container_push

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

There are no tests for container_push, didn't explore adding those, in terms of docs the documented behaviour is not what's happening, after this PR docs and behaviour matches.

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Workspace configures toolchain with both client_config and cred_helpers but yet the container_push is not authenticated, unless the helpers are in the host $PATH, leading to non reproducible setups.

Issue Number: 2126

What is the new behavior?

Workspace configures toolchain with both client_config and cred_helpers but now the provided cred_helpers are used for authentication not relying on host setup.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Using it internally at booking.com already

[manuelnaranjo]

@uhthomas maybe you can review? CI is not passing because of ubuntu 22.04 issues

[github-actions]

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