refactor: define new Synchronizer and Initializer interfaces for FDv2 #2736

Job	Run time
build-test-client-windows-curl	15m 39s
contract-tests	3m 1s
contract-tests-curl	3m 22s
build-test-client-mac-curl	4m 43s
build-test-curl	6m 8s
build-test	5m 47s
build-test-client-mac	5m 0s
build-test-client-windows	14m 26s
	58m 6s

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