Adds transfers between stores to external attachments #3380

Job	Run time
build_and_test (3.11, 22.x, :lint:python:client:common:smoke:stubs:)	5m 10s
build_and_test (3.11, 22.x, :server-1-of-2:)	7m 24s
build_and_test (3.11, 22.x, :server-2-of-2:)	9m 37s
build_and_test (3.11, 22.x, :gen-server:)	3m 36s
build_and_test (3.11, 22.x, :nbrowser-^[A-D]:)	10m 51s
build_and_test (3.11, 22.x, :nbrowser-^[E-L]:)	9m 46s
build_and_test (3.11, 22.x, :nbrowser-^[M-N]:)	11m 54s
build_and_test (3.11, 22.x, :nbrowser-^[O-R]:)	4m 44s
build_and_test (3.11, 22.x, :nbrowser-^[^A-R]:)	7m 34s
build_and_test (:lint:python:client:common:smoke:, 22.x, 3.10)	4m 49s
candidate	0s
	1h 15m 25s

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