feat: add Batcher#close(timeout) and Batcher#cancelOutstanding #8022

Job	Run time
build(21) except self-service clients	13m 52s
build(8) except for gapic-generator-java	4m 22s
build (11)	14m 50s
build (17)	15m 6s
build(8) for gapic-generator-java	11m 54s
lint	27s
showcase (11)	4m 6s
showcase (17)	4m 0s
showcase (21)	4m 6s
compatibility	1m 41s
gapic-generator-java-bom	1m 44s
dependency_analyzer_unit_test	14s
showcase-clirr	3m 17s
showcase-native	8m 8s
unmanaged_dependency_check	3m 54s
	1h 31m 41s

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