build: add option to force regenerate all #17223

Job	Run time
owlbot-yaml	1m 0s
owlbot-py	1m 10s
package_name_check	1m 0s
generate-readme	1m 6s
gapic-bom	1m 42s
gitignore_correctness	1m 1s
group_id_check_for_maps_libraries	8m 22s
root-pom	1m 41s
	17m 2s

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