Support AWS RDS Aurora Serverless Instances

[fogfish]

As a user I want to use the tool together with AWS RDS Aurora Serverless so that there is a complete view on the status of my cluster

I think long-term solution would be to display ACU per cluster.

The view could look like this (RESOURCES column instead of CPU and MEM)

AZ ENGINE            VSN    INSTANCE        RESOURCES       STORAGE TYPE   RO NAME
   aurora-postgresql 15.3                   120 ACU                           example-production
1b aurora-postgresql 15.3   db.serverless                   1 GiB aurora      example-production-instance-1
1a aurora-postgresql 15.3   db.serverless                   1 GiB aurora   ro example-production-instance-2
   aurora-postgresql 13.8                   4 ACU                             example-stage
1a aurora-postgresql 13.8   db.serverless                   1 GiB aurora      example-stage-instance-1
1a postgres          13.10  db.t4g.small    2 vCPU / 4 GiB  20 GiB gp3        single-instance

This can be achieved by calling DescribeDBClusters and looking up the corresponding field based on the cluster type:

Serverless v1: Capacity Serverless v2: ServerlessV2ScalingConfiguration Limitless Database: LimitlessDatabase