chore: explore parallel library generation #17800

Job	Run time
owlbot-yaml	58s
group_id_check_for_maps_libraries	8m 34s
gapic-bom	1m 20s
package_name_check	49s
owlbot-py	1m 15s
generate-readme	1m 12s
root-pom	1m 47s
gitignore_correctness	42s
	16m 37s

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