Modify BackupPolicy CRD to include s3 prefix

[pasquale1981]

What

At the moment it seems that I can't set a prefix for the backup location. It's just possible to set the bucket name, than moco will create the "moco" prefix (moco/namespace/mysql-db-name).
The use-case is for example when you have one s3 bucket, and inside that bucket you have one prefix for k8s cluster.
So it would be great if you could set up moco to send the backups to bucket-name/cluster-name/moco etc..

should be something like this:

  bucketConfig:
      bucketName: my-backup-bucket
      region: eu-west-1
      prefix: my-cluster-name
      usePathStyle: true

[ymmt2005]

sounds like a reasonable use case.