resource/aws_db_cluster_snapshot: Add plan-time validation for db_cluster_snapshot_identifier argument (#15132)
resource/aws_db_cluster_snapshot: Add plan-time validation for db_cluster_snapshot_identifier argument (#15132)

Output from acceptance testing:

```
--- PASS: TestAccAWSDBClusterSnapshot_basic (177.55s)
--- PASS: TestAccAWSDBClusterSnapshot_Tags (194.42s)
```
terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws