feat: Add experimental S2A integration in client libraries grpc transport #9057

Job	Run time
build(8) except for gapic-generator-java	4m 25s
build(21) except self-service clients	12m 3s
build (11)	12m 50s
build (17)	12m 59s
build(8) for gapic-generator-java	9m 43s
lint	28s
compatibility	1m 46s
dependency_analyzer_unit_test	31s
gapic-generator-java-bom	2m 5s
showcase (11)	4m 24s
showcase-clirr	3m 11s
showcase (17)	4m 16s
showcase-native	8m 48s
showcase (21)	4m 16s
unmanaged_dependency_check	5m 16s
	1h 27m 1s

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