[python] Extract _write_manifest_file in FileStoreCommit #202

Job	Run time
requirement_version_compatible_test	4m 44s
torch_test	1m 23s
build_native / build_native	1m 51s
lint-python (3.6.15)	17m 17s
lint-python (3.10)	19m 33s
	44m 48s

Provide feedback