Merge pull request #28361 from hashicorp/b-aws_db_instance.gp3-again

r/aws_db_instance: gp3 storage documentation additions

Author: ewbankkit

website/docs/r/db_instance.html.markdown

@@ -149,6 +149,8 @@ identifier beginning with the specified prefix. Conflicts with `identifier`.
 * `instance_class` - (Required) The instance type of the RDS instance.
 * `iops` - (Optional) The amount of provisioned IOPS. Setting this implies a
 storage_type of "io1". Can only be set when `storage_type` is `"io1"` or `"gp3"`.
+Cannot be specified for gp3 storage if the `allocated_storage` value is below a per-`engine` threshold.
+See the [RDS User Guide](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Storage.html#gp3-storage) for details.
 * `kms_key_id` - (Optional) The ARN for the KMS encryption key. If creating an
 encrypted replica, set this to the destination KMS ARN.
 * `license_model` - (Optional, but required for some DB engines, i.e., Oracle
@@ -217,7 +219,7 @@ default is `false` if not specified.
 purpose SSD), "gp3" (general purpose SSD that needs `iops` independently)
 or "io1" (provisioned IOPS SSD). The default is "io1" if `iops` is specified,
 "gp2" if not.
-* `storage_throughput` - (Optional) The storage throughput value for the DB instance. Can only be set when `storage_type` is `"gp3"`.
+* `storage_throughput` - (Optional) The storage throughput value for the DB instance. Can only be set when `storage_type` is `"gp3"`. Cannot be specified if the `allocated_storage` value is below a per-`engine` threshold. See the [RDS User Guide](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Storage.html#gp3-storage) for details.
 * `tags` - (Optional) A map of tags to assign to the resource. If configured with a provider [`default_tags` configuration block](https://registry.terraform.io/providers/hashicorp/aws/latest/docs#default_tags-configuration-block) present, tags with matching keys will overwrite those defined at the provider-level.
 * `timezone` - (Optional) Time zone of the DB instance. `timezone` is currently
 only supported by Microsoft SQL Server. The `timezone` can only be set on