Periodically pause copying ledger nodes during online_delete #4219

Job	Run time
dependencies (linux, gcc, Debug)	3m 15s
dependencies (linux, gcc, Release)	2m 20s
dependencies (linux, clang, Debug)	2m 52s
dependencies (linux, clang, Release)	2m 19s
conan	2m 53s
coverage (linux, gcc, Debug)	13m 43s
test (linux, gcc, Debug)	11m 12s
test (linux, gcc, Debug, -Dunity=ON)	7m 54s
test (linux, gcc, Release)	12m 32s
test (linux, gcc, Release, -Dunity=ON)	8m 22s
test (linux, clang, Debug)	9m 6s
test (linux, clang, Debug, -Dunity=ON)	6m 30s
test (linux, clang, Release)	11m 8s
test (linux, clang, Release, -Dunity=ON)	8m 17s
	1h 42m 23s

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