No way to specify custom lifecycle key for persistent container

Tests might need to set up and use persistent, shared container for multiple test runs. DCP has support for this via custom `LifecycleKey` but that `Container` property is not exposed via Aspire app model API.

We should add an API that allows to set the lifecycle key, and we should also document/expose as a constant the label that DCP is using for storing the lifecycle key on the "physical" container.