feat: add code samples for secret manager access by alias (#373)

* feat: add code samples for secret manager access by alias

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

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