What does this PR address?

This PR fixes an issue where BentoML containers fail to start in Kubernetes when using an exec-style entrypoint like:

command: ["bentoml", "serve"]

The failure occurs because the bentoml CLI binary is installed inside a virtual environment at /app/.venv/bin, which is not included in the default $PATH. While the binary is available interactively (e.g., via kubectl exec), it is not found during container startup using Kubernetes command: override.

This PR updates the Dockerfile generation logic to include /app/.venv/bin in the $PATH by injecting it through the bento__envs mechanism. This ensures that the Bento container works seamlessly with Kubernetes-style overrides.

Fixes

Fixes #5310

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