Support for io2 storage type

[vmercierfr]

Is your feature request related to a problem? Please describe

Amazon RDS now supports io2 Block Express, but Prometheus RDS exporter don't support it yet.

Describe the solution you'd like

Prometheus RDS exporter should support this new storage class

Describe alternatives you've considered

n/a

Additional context

• https://docs.aws.amazon.com/ebs/latest/userguide/provisioned-iops.html#io2-block-express
• https://aws.amazon.com/fr/about-aws/whats-new/2024/03/amazon-rds-io2-block-express-sub-millisecond-latency-99-999-durability/