chore: add generation config #6855

Job	Run time
build(8) for gapic-generator-java	9m 30s
build(8) except for gapic-generator-java	4m 10s
build(21) except self-service clients	11m 56s
build (11)	12m 40s
build (17)	12m 33s
compatibility	1m 32s
dependency_analyzer_unit_test	22s
gapic-generator-java-bom	1m 50s
lint	26s
showcase (11)	3m 47s
showcase (17)	4m 2s
showcase-clirr	3m 5s
showcase-native	8m 5s
unmanaged_dependency_check	4m 2s
	1h 18m 0s

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