docs: Create a guide for endpoint and universe domain #14401

Job	Run time
generate-readme	44s
group_id_check_for_maps_libraries	5m 50s
gapic-bom	1m 13s
root-pom	1m 15s
owlbot-py	40s
gitignore_correctness	33s
package_name_check	34s
owlbot-yaml	33s
	11m 22s

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