chore(hermetic-build): explore parallel generation #17795

Job	Run time
owlbot-yaml	1m 0s
owlbot-py	1m 13s
gapic-bom	1m 50s
root-pom	1m 46s
generate-readme	1m 8s
package_name_check	1m 5s
gitignore_correctness	1m 5s
group_id_check_for_maps_libraries	8m 6s
	17m 13s

Provide feedback