feat(compute): Regional disk samples

[Shnatsel]

To go on this page: https://cloud.google.com/compute/docs/disks/regional-persistent-disk

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• compute/disks/attach_regional_disk.go:17, tag compute_regional_disk_attach
• compute/disks/attach_regional_disk_readonly.go:17, tag compute_regional_disk_attach_read_only
• compute/disks/resize_regional_disk.go:17, tag compute_regional_disk_resize

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