Create update_secret_with_alias.php

[nataliesalvati]

Update samples for Access By Alias Launch

[snippet-bot]

Here is the summary of changes.

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• secretmanager/src/update_secret_with_alias.php:28, tag secretmanager_update_secret_with_alias

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[bshaffer]

This looks good but it needs a test!

[nataliesalvati]

Think I've updated the test properly.