Provide a simple way to configure minio pools
### Summary
Since minio pools have to be provided as a list to the helm chart, they are hard to overload by end users (the whole pool configuration has to be provided)
It is indeed very common to need to override the server count (as it is immutable, and currently configured dynamically depending on the amount of nodes), or the volume size.
We should provide high level parameters to allow the configuration of these values.
issue