Saga pantry attach/detach: fail if pantry is removed from DNS #38750

Job	Run time
check-omicron-deployment (ubuntu-22.04)	3m 8s
check-features	5m 50s
check-omicron-deployment (macos-14)	3m 36s
check-style	20s
build-docs	3m 43s
clippy-lint	5m 42s
	22m 19s

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