[BUG] Detection of command container fails if no command is present

[trvrnrth]

Describe the bug

Detection of the command container fails if no command is specified for a step. This can often be the case when using the docker-compose plugin if the command is specified in docker-compose.yml and thus not required in the step itself. This breaks use of a custom image for the step and application of resource class requests/limits.

To Reproduce

Example step:

  - name: 'Test'
    agents:
      resource_class: large-amd64
    plugins:
      docker-compose#v5.12.1:
        run: test

Expected behavior

Resource class requests/limits are applied.

Environment

• agent-stack-k8s version: 0.37.1
• Kubernetes version: 1.34
• Deployment method: Helm chart

Logs

n/a

Additional context

I suspect the check could perhaps just check for the existence of the env var and accept that it may be empty?

[zhming0]

Thank you @trvrnrth . I combined your commit with mine in #818. We will make a release soon!