Add async APIs for shutting down the databases #1026

Job	Run time
linux-integration-psql	3m 52s
linux-integration-mysql	3m 30s
linux-integration-mongo	3m 14s
linux-integration-sqlite	2m 10s
unit-tests / api-breakage	3m 21s
unit-tests / linux-unit (swift:5.8-jammy)	1m 50s
unit-tests / linux-unit (swift:5.9-jammy)	2m 4s
unit-tests / linux-unit (swift:5.10-noble)	2m 34s
unit-tests / macos-unit (macos-13, ~15.2)	2m 34s
unit-tests / linux-unit (swiftlang/swift:nightly-6.0-jammy)	2m 57s
unit-tests / macos-unit (macos-14, latest-stable)	1m 46s
unit-tests / linux-unit (swiftlang/swift:nightly-main-jammy)	2m 44s
	32m 36s

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