Support for turbo replication

[iainlbc]

TL;DR

Would like the ability to enable turbo replication on the bucket resource created by this module (we are using the simple bucket module primarily):

(Optional) The recovery point objective for cross-region replication of the bucket. Applicable only for dual and multi-region buckets. "DEFAULT" sets default replication. "ASYNC_TURBO" value enables turbo replication, valid for dual-region buckets only. See [Turbo Replication](https://cloud.google.com/storage/docs/managing-turbo-replication) for more information. If rpo is not specified at bucket creation, it defaults to "DEFAULT" for dual and multi-region buckets. NOTE If used with single-region bucket, It will throw an error.

-- https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/storage_bucket.html#rpo

Terraform Resources

https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/storage_bucket.html#rpo

Detailed design

No response

Additional information

https://cloud.google.com/storage/docs/availability-durability#turbo-replication