FR: Add sample for dual-region bucket creation.

The sample for creating a bucket should accept a bucket name and 2 regions (e.g. my-bucket, US-EAST1, US-WEST1).

Region tag: storage_create_bucket_dual_region

System tests:

• Verify a dual region bucket with specified regions can be created
• Verify a dual region bucket's location metadata is the specified dual region provided
• Verify a dual region bucket's locationType metadata is dual-region

[Internal]

• For canonical samples: go/dual-region-canonical-sample
• For details and coordination: go/gcs-dpe-dual-region-milestones