feat(storage transfer): Added samples for storage transfer

[thiyaguk09]

• Add quickstart samples for sts
• Add nearline samples for sts
• Add posix and manifest samples for sts
• Add check latest transfer operation samples for sts
• Add transfer from posix samples for sts

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• storagetransfer/src/check_latest_transfer_operation.php:20, tag storagetransfer_get_latest_transfer_operation
• storagetransfer/src/manifest_request.php:20, tag storagetransfer_manifest_request
• storagetransfer/src/nearline_request.php:20, tag storagetransfer_transfer_to_nearline
• storagetransfer/src/posix_request.php:20, tag storagetransfer_transfer_from_posix

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