docs: fix misdocumentation about helmfile prod activation

The production environment is the final deployment environment associated with your production branch (`main` or `master` by default).

It is **enabled by default** and can be disabled by setting the `HELMFILE_PROD_DISABLED` variable (see below).

It is **disabled by default** and can be disabled by setting the `HELMFILE_PROD_ENABLED` variable (see below).

Here are variables supported to configure the production environment:

| Input / Variable | Description                            | Default value     |

| ------------------------ | -------------------------------------- | ----------------- |

| `HELMFILE_PROD_DISABLED` | Set to `true` to disable `production` env | _none_ (disabled)  |

| `HELMFILE_PROD_ENABLED` | Set to `true` to enable `production` env | _none_ (disabled)  |

| `prod-app-name` / `HELMFILE_PROD_APP_NAME` | Application name for `production` env  | `$HELMFILE_BASE_APP_NAME` |

| `prod-environment-url` / `HELMFILE_PROD_ENVIRONMENT_URL`| The production environment url _(only define for static environment URLs declaration and if different from default)_ | `$HELMFILE_ENVIRONMENT_URL` |

| `prod-namespace` / `HELMFILE_PROD_NAMESPACE` | The Kubernetes namespace to use for `production` env _(only define to override default)_ | `$KUBE_NAMESPACE` |