feat: update apikey sample for client option support

[bshaffer]

Sample for googleapis/gax-php#351

[bshaffer]

note: kokoro tests are not running due to an ACL failure, but I have run the tests locally and confirmed they pass

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• auth/src/auth_cloud_apikey.php:23, tag apikeys_authenticate_api_key

You are about to delete 1 region tag.

• auth/src/auth_cloud_apikey.php:23, tag auth_cloud_apikey

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