Support a single target resource for doneness/deletion trigger

Single deletion target

In the llm-d project we have an interesting problem where we need to deploy pretty often:

1. 2 Deployments or LWS (using Kueue for this solves a lot of resource coordination problems with experiments)
2. A Job containing a simulated inference workload (like guidellm) or unit tests
3. A whole bunch of other configuration resources that can also be ephemeral but aren't scheduleable

It's my understanding that the AppWrapper never exits because the Deployments are never considered to be done.

It would be a great feature to allow defining a single target resource that is used to garbage collect everything else in the AppWrapper, then I wouldn't have to include a poison pill or self-destruct script that triggers after the benchmark is complete to tear down the inference deployment. I would set the target deletion resource to be the Job.

Start in the AppWrapper controller's doneness and deletion handling, focusing on how Deployments, LWS resources, and Jobs are evaluated. Trace how an AppWrapper currently reaches completion and how its resources are garbage-collected. Done means a configured Job or other single target can trigger cleanup of the remaining AppWrapper resources without a poison pill or self-destruct script.