chore: migrate sdk-platform-java to monorepo #64

Job	Run time
filter	1m 14s
build(25) except self-service clients	4m 31s
build(21) except self-service clients	4m 23s
build(8) for showcase	9m 18s
build(8) for gapic-generator-java	2m 24s
build (17)	4m 51s
showcase-clirr	1m 38s
build (11)	4m 46s
gapic-generator-java-bom	3m 1s
showcase (25)	2m 43s
dependency_analyzer_unit_test	1m 18s
showcase (11)	2m 41s
build(8) except for gapic-generator-java	4m 2s
showcase (21)	2m 27s
showcase (17)	2m 43s
unmanaged_dependency_check	7m 16s
	59m 16s

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