fix: bump hashicorp/aws to 5.61.0 (#255)

* fix: bump `hashicorp/aws` min to 5.61.0

`hashicorp/aws` needs to be at least [5.61.0](https://github.com/hashicorp/terraform-provider-aws/releases/tag/v5.61.0) to support `performance_insights_enabled` in `aws_rds_cluster`.

* docs: update README

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Co-authored-by: Lennart Goedhart <lgoedhart-ic@akiliinteractive.com>

Author: pazaan