Worker: inject Dynamic ENVVAR via Lifecycle Hook

[takaoka-youta-opst]

Inject arbitary Environmental Variables into Run Worker.

Currently, no ENVVARs are supported on runtime.

This proposal proposes:

• Lifecycle Hook before "starting" can response ENVVAR
• Knitfab injects the ENVVARs in response into Worker pod.

Motivation

For example, let us think about to integrate with MLFlow. Worker should know Tracking Server URI and Run ID or Experiment ID to log parameters/metrics with MLFlow. If associating "Knitfab Run and MLFlow Run" and "Knitfab Plan and MLFlow Experiment", MLFLOW_* ENVVAR should be determined from a Knitfab Run in dynamic way.

Other integrations using ENVVAR may be with same vives.

Spec

If Response of Lifecycle Hook before "starting" is Content-Type: application/json and formatted in

{
    "env": {[key: string]: string}
}

, Knitfab uses env content as ENVVARs to be injected to Worker pod.

[takaoka-youta-opst]

The type proposed in "Spec" is too simple, and I afraid to conflict with existing hook implementation responsing something.

So, I change type as follow:

{
    "knitfabExtension": {
        "env": {[key: string]: string}
    }
}

Key "knitfabExtension" is a "namespace" for Knitfab Hooks to refer.