chore: add generation config #6836

Job	Run time
build(21) except self-service clients	11m 18s
build (11)	12m 46s
build (17)	12m 50s
build(8) except for gapic-generator-java	4m 8s
build(8) for gapic-generator-java	9m 43s
compatibility	1m 31s
lint	23s
dependency_analyzer_unit_test	19s
gapic-generator-java-bom	1m 46s
showcase (11)	4m 3s
showcase (17)	3m 59s
showcase-clirr	3m 1s
showcase-native	8m 10s
unmanaged_dependency_check	5m 58s
	1h 19m 55s

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