chore: add librarian.yaml to google-cloud-java #19347

Job	Run time
generate-readme	1m 32s
root-pom	1m 44s
package_name_check	1m 7s
owlbot-py	1m 26s
group_id_check_for_maps_libraries	9m 29s
owlbot-yaml	1m 10s
gitignore_correctness	1m 19s
gapic-bom	1m 59s
	19m 46s

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