pool: add GetInstances method, that returns current instances connections state #4075

Job	Run time
run-tests-ce (1.20, 1.10, false, false)	4m 33s
run-tests-ce (1.20, 2.8, false, false)	4m 17s
testing_mac_os (1.20, macos-13, brew)	6m 31s
run-tests-ce (1.20, 2.10, false, false)	4m 49s
testing_mac_os (1.20, macos-13, 1.10.15)	11m 25s
run-tests-ce (1.20, master, false, false)	5m 8s
run-tests-ce (stable, 1.10, false, false)	4m 17s
testing_mac_os (1.20, macos-14, brew)	4m 21s
run-tests-ce (stable, 2.8, false, false)	4m 29s
testing_mac_os (stable, macos-13, brew)	5m 34s
run-tests-ce (stable, 2.10, false, false)	4m 49s
testing_mac_os (stable, macos-13, 1.10.15)	9m 4s
run-tests-ce (stable, master, false, false)	5m 10s
testing_mac_os (stable, macos-14, brew)	4m 24s
run-tests-ce (master, true, 1.20)	6m 42s
run-tests-ce (master, true, 1.20, false)	5m 33s
	1h 31m 6s

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