Add flush cause metric #9088

Job	Run time
unit-test (8, ubuntu-latest, others)	16m 36s
unit-test (8, ubuntu-latest, datanode)	26m 40s
unit-test (8, windows-latest, others)	19m 21s
unit-test (8, windows-latest, datanode)	44m 41s
unit-test (17, ubuntu-latest, others)	17m 50s
unit-test (17, ubuntu-latest, datanode)	26m 43s
unit-test (17, windows-latest, others)	21m 22s
unit-test (17, windows-latest, datanode)	35m 45s
unit-test (17, macos-latest, datanode)	47m 2s
unit-test (17, macos-latest, others)	16m 20s
	4h 32m 20s

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