make RDS backup retention configurable

when provisioning RDS with cloudformation, the number of backups is hardcoded to 5 under

cloudformation/infra-db.yaml:Resources.DBCluster.Properties.BackupRetentionPeriod

can you please:

• make this configurable for v2 CF deployments in config.json

• make this configurable for v3 reference architecture, e.g. in tf modules [note that EKS module has create_database switch, while ECS module is missing it - I have reported that separately]