feat(storage): sample for autoclass

[vishwarajanand]

Addresses: https://github.com/GoogleCloudPlatform/php-docs-samples/issues/1682 (couldn't test in local, since feature not enabled in my gcp proj)

Design doc: go/php-storage-autoclass PR for python: https://github.com/googleapis/python-storage/pull/791

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 2 region tags.

• storage/src/get_bucket_autoclass.php:26, tag storage_get_autoclass
• storage/src/set_bucket_autoclass.php:26, tag storage_set_autoclass

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[vishwarajanand]

Update: To be merged in the first week of Nov.