service/docdb/types: DBCluster is missing support for TagList

[xinau]

Confirm by changing [ ] to [x] below to ensure that it's a bug:

• [x] I've gone though the API reference
• [x] I've checked AWS Forums and StackOverflow for answers
• [x] I've searched for previous similar issues and didn't find any solution

Describe the bug The DocumentDB cluster type doesn't include support tags on the resource even though they can be seen and specified in AWS. The types module includes a type Tag but this isn't used anywhere inside the types module.

Version of AWS SDK for Go? v1.5.0

To Reproduce (observed behavior) The DocumentDB cluster struct doesn't include a list of tags. https://github.com/aws/aws-sdk-go-v2/blob/4a50e355e38285ae39efeb73fd5ef517c4f45cae/service/docdb/types/types.go#L56-L170

Expected behavior A list of tags should be available on the resource similar to other RDS and other resources.