Adds transfers between stores to external attachments #3382

Job	Run time
build_and_test (3.11, 22.x, :lint:python:client:common:smoke:stubs:)	5m 46s
build_and_test (3.11, 22.x, :server-1-of-2:)	7m 17s
build_and_test (3.11, 22.x, :server-2-of-2:)	9m 36s
build_and_test (3.11, 22.x, :gen-server:)	3m 40s
build_and_test (3.11, 22.x, :nbrowser-^[A-D]:)	10m 34s
build_and_test (3.11, 22.x, :nbrowser-^[E-L]:)	9m 26s
build_and_test (3.11, 22.x, :nbrowser-^[M-N]:)	11m 49s
build_and_test (3.11, 22.x, :nbrowser-^[O-R]:)	4m 40s
build_and_test (3.11, 22.x, :nbrowser-^[^A-R]:)	7m 3s
build_and_test (:lint:python:client:common:smoke:, 22.x, 3.10)	5m 17s
candidate	0s
	1h 15m 8s

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