[snapshots] split db download and formal download snapshot commands #57998

Job	Run time
diff	8s
license-check	1m 13s
release-notes-check	5s
test (ubuntu-ghcloud)	12m 44s
clippy	4m 41s
simtest	12m 38s
test-extra (ubuntu-ghcloud)	15m 25s
windows-build (windows-ghcloud)	16m 38s
cargo-deny (advisories, licenses, bans, ...)	3m 10s
graphql-rpc	19m 29s
move-test	0s
rustfmt	18s
cutting a new execution layer	3m 57s
test-extra	0s
test	0s
	1h 30m 26s

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