Migrate configuration to the config api and remove the env vars

[ahg-g]

The configuration api is ready to be used for configuring the epp, we should use that by default and update the helm chart.

I recommend offering a couple of canned configurations created as configmaps that a user can select from: the default and what we call v2 scheduler.

To be able to use the chart by other projects that customize EPP (like llm-d), the helm chart should allow creating the configmap from a remote path (like a published release configmap manifest)

[ahg-g]

This issue is only to track the migration of the flags to the config api; I created a separate issue for updating the helm chart: #1137