Support for volume expansion

[xoxys]

This feature was initially requested in https://github.com/minio/operator/issues/310 already, but the issue got staled.

With the latest operator, this does not seem to work properly. After updating the volumeClaimTemplate.spec.resources.requests.storage of a pool from 2Gi to 5Gi, the value in StatefulSet or PersistentVolumeClaim is still not updated and remains at the old value.

[xoxys]

Updating the PersistentVolumeClaim manually and restarting the StatefulSet works.

[cesnietor]

@jiuker I saw a PR sent for this but got closed, what's the current status of it? cc @pjuarezd

[jiuker]

fixed by #2196