feat: add common logic for supporting universe domain (#621)

* add common logic for supporting universe domain

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* fix lint issues

* add dependency to oauth2client

* update test cases

* remove dependency to oauth2client

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* fix lint issues

* updates to universe helpers

* update module name and make methods public

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* update lint issues

* address PR comments

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* use empty universe error in test cases

* remove mtls error and add test cases

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* remove is True from test cases

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Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>