storage/buckets: Update Dual-Region Bucket Creation Sample to Output Additional Metadata

[danielbankhead]

We want to update the dual-region samples to uniformly include location, locationType, and customPlacementConfig metadata in the output.

This should be a small change to: https://github.com/GoogleCloudPlatform/golang-samples/blob/HEAD/storage/buckets/create_bucket_dual_region.go

Here's an example from Node.js storage: https://github.com/googleapis/nodejs-storage/pull/2016