chore: migrate sdk-platform-java to monorepo #16603

Job	Run time
owlbot-yaml	1m 4s
package_name_check	57s
gapic-bom	1m 51s
root-pom	1m 43s
gitignore_correctness	1m 4s
owlbot-py	1m 14s
group_id_check_for_maps_libraries	7m 32s
generate-readme	1m 11s
	16m 36s

Provide feedback