Adds transfers between stores to external attachments #3504

Job	Run time
build_and_test (3.11, 22.x, :lint:python:client:common:smoke:stubs:)	5m 6s
build_and_test (3.11, 22.x, :server-1-of-2:)	3m 39s
build_and_test (3.11, 22.x, :server-2-of-2:)	10m 12s
build_and_test (3.11, 22.x, :gen-server:)	5m 37s
build_and_test (3.11, 22.x, :nbrowser-^[A-D]:)	11m 20s
build_and_test (3.11, 22.x, :nbrowser-^[E-L]:)	9m 49s
build_and_test (3.11, 22.x, :nbrowser-^[M-N]:)	12m 17s
build_and_test (3.11, 22.x, :nbrowser-^[O-R]:)	5m 7s
build_and_test (3.11, 22.x, :nbrowser-^[^A-R]:)	7m 22s
build_and_test (:lint:python:client:common:smoke:, 22.x, 3.10)	5m 10s
candidate	0s
	1h 15m 39s

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