Previously, tags were only available via rds:ListTagsForResource, but are now
included in the Create/DescribeDBInstance responses as of Botocore 1.18.17[1]
[1]: f29d23c53e (diff-d10722c0e11ded323c8d240066d7ed31e93a1e6423d54e091b7d54b86e6bd4e0)
Fixes #3458