Adds transfers between stores to external attachments #3377

Job	Run time
build_and_test (3.11, 22.x, :lint:python:client:common:smoke:stubs:)	2m 27s
build_and_test (3.11, 22.x, :server-1-of-2:)	2m 0s
build_and_test (3.11, 22.x, :server-2-of-2:)	1m 30s
build_and_test (3.11, 22.x, :gen-server:)	1m 39s
build_and_test (3.11, 22.x, :nbrowser-^[A-D]:)	1m 29s
build_and_test (3.11, 22.x, :nbrowser-^[E-L]:)	1m 37s
build_and_test (3.11, 22.x, :nbrowser-^[M-N]:)	1m 25s
build_and_test (3.11, 22.x, :nbrowser-^[O-R]:)	1m 38s
build_and_test (3.11, 22.x, :nbrowser-^[^A-R]:)	1m 35s
build_and_test (:lint:python:client:common:smoke:, 22.x, 3.10)	2m 21s
candidate	0s
	17m 41s

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