feat(observability): Implement gcp.client.service attribute #17118

Job	Run time
gitignore_correctness	1m 5s
owlbot-py	1m 11s
gapic-bom	1m 40s
owlbot-yaml	1m 4s
package_name_check	1m 3s
generate-readme	1m 6s
group_id_check_for_maps_libraries	7m 40s
root-pom	1m 47s
	16m 36s

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