Use Zone UUID as Dataset UUID in RSS

[smklein]

Potential fix for #7265

[smklein]

I think this PR, as-is, is still wrong -- I think that it also needs to ensure all future dataset UUIDs associated with zones get a value of "Dataset UUID" set to the "Zone UUID", otherwise the sled-agent overwrite will ignore the "new" blueprint value:

Source of "sled agent overwrite":
https://github.com/oxidecomputer/omicron/blob/main/sled-agent/src/sled_agent.rs#L965-L970

Spots in reconfigurator planning where we'd need to also ensure that the "new dataset UUIDs == zone UUIDs":

omicron/nexus/reconfigurator/planning/src/blueprint_editor/sled_editor/datasets.rs

Lines 390 to 393 in 4a4d6ca

	rng.next_dataset()
	}
	} else {
	rng.next_dataset()

[smklein]

Preferring to not do this solution, abandoning