Concurrent transfers from a MedusaConfiguration is always overridden by 1

[adejanovski]

The Medusa storage properties defined in a K8ssandraCluster spec use 1 as kubebuilder default for concurrent_transfers. As this is not the "zero value" for integers, it always wins against the value defined in a MedusaConfiguration.

In order to fix this, while retaining the priority of the storage properties over the MedusaConfiguration, we need to modify the default and set it to 0, and modify the code that generates the medusa.ini configmap entry to swap 0 for 1 in case it wasn't defined in either the MedusaConfiguration nor the storage properties.

Definition of Done

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1. K8ssandra.spec.medusa.storageProperties.concurrentTransfers defaults to 0 instead of 1 (see here)
2. Before persisting the medusa.ini to the configmap in the K8ssandraCluster reconcile, swap 0 for 1 if that is the value we get out of the Goalesce merge