Sled Agent: API to manage datasets independently of zones #6042
Description
We need this explicitly for support bundles, but there is a precedent for requesting zones.
In the API exposed by sled agent, we currently expose an API to "ensure zones". This API creates, but never deletes, datasets.
We should have datasets be controlled separately from zones -- this will let the sled agent manage them explicitly, and expose them more easily to Nexus.
Related to #2000