Postgres Aurora Integration IAM authentication is enabled by default

[mbyio]

Additional environment details (Operating System, Cloud provider, etc):

Using AWS, Kubernetes, Datadog helm chart 3.57.3, and configured the postgres integration using a cluster check.

Steps to reproduce the issue:

1. Make an aurora serverless postgres DB with IAM authentication disabled
2. Create Datadog user
3. Run on a K8s node without the default metadata service disabled (so the node IAM role can be assumed by a pod)
4. Create a K8s service and annotation to connect to postgres
5. Add an aws section to the config, specify the instance_endpoint and region fields, but nothing else
6. Cluster check fails in logs with "password authentication failed for user datadog..." even though I confirmed the correct password is set
7. After adding managed_authentication: {"enabled": false}, it started working

Describe the results you received:
IAM authentication enabled by default

Describe the results you expected:
IAM authentication not enabled by default (this is what the docs say is the default)

Additional information you deem important (e.g. issue happens only occasionally):