Function prepare_build_command

pub fn prepare_build_command(
    image: &str,
    dockerfile: &Path,
    features: Option<&[String]>,
) -> Command

Construct (but do not run) the docker build command for a test-runner image.

• image is the full tag (e.g. "vector-test-runner-1.86.0:latest").
• dockerfile is the path to the Dockerfile (e.g. scripts/integration/Dockerfile).
• features controls the FEATURES build-arg (pass None for an empty list).