Provider specific configuration schema

I want to be able to configure each provider in the config file. Right now that configuration happens through environment variables.

```json
{
  "node": {
    "version": "24",
    "packageManager": "bun"
  },
  "python": {},
}
```

Each provider could expose a JSON schema that is added to the https://schema.railpack.com so that you get editor autocomplete.