feat(observability): implement url.domain attribute #17178

Job	Run time
gapic-bom	1m 48s
gitignore_correctness	1m 4s
owlbot-yaml	1m 6s
group_id_check_for_maps_libraries	8m 17s
package_name_check	1m 4s
root-pom	1m 40s
owlbot-py	1m 14s
generate-readme	1m 16s
	17m 29s

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