chore(sdk-platform-java): restore GEMINI.md and DEVELOPMENT.md #596

Job	Run time
filter	1m 2s
build(8) except for gapic-generator-java	3m 58s
build (11)	14m 1s
build (17)	13m 34s
build(8) for gapic-generator-java	11m 25s
build(8) for showcase	9m 35s
unmanaged_dependency_check	7m 38s
build(21) except self-service clients	12m 8s
build(25) except self-service clients	12m 29s
showcase-clirr	5m 12s
gapic-generator-java-bom	2m 6s
dependency_analyzer_unit_test	1m 18s
showcase (17)	10m 32s
showcase (25)	10m 20s
showcase (11)	10m 48s
showcase (21)	10m 13s
	2h 16m 19s

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