Creates a single long-running parent job that orchestrates subscription-level import jobs.
The parent job discovers subscriptions, dispatches child import jobs (one per subscription),
aggregates progress, and determines overall success/failure.

Two modes are supported:

1. Import All: Set importAll: true to discover all subscriptions and import all resources
2. Selective Import: Provide specific subscriptions and resource IDs to import

Selective imports default to reconcile behavior: subscriptions and resources omitted from the request
are soft-deleted. Set importMode to Additive for host-pool-only imports that must preserve
all existing managed resources.

When importing, CloudSubscription records are automatically created for Azure subscriptions
that don't exist yet in the system. These subscriptions are linked to the tenant and use
the tenant's default credentials.