Solutions that include Portworx or ODF on IBM Cloud cannot be destroyed cleanly

The volumes are left hanging around and prevent the resource group from being destroyed. A separate issue has been opened with the resource group module to address the destroy failure if volumes remain - https://github.com/cloud-native-toolkit/terraform-ibm-resource-group/issues/58

We need a way to destroy the volumes if a `purge_volumes` variable is set. This flag would be set to `false` by default but always set to `true` in our automation tests. The question is where this flag should be defined. Options are:

Option>ProsCons

VPC module

• Volumes are VPC resources


• When the VPC is destroyed likely done with the volumes

• Not sure we can easily tell with which VPC a volume is associated

Cluster module

• Volumes are associated with the cluster through a tag and can be identified

• The point of saving the volumes is so the data can be preserved and restored when one cluster is destroyed and a new one is created in its place

Resource group module

• When the resource group is destroyed then it can be assumed the volume is no longer needed

• Volume management is outside the scope of the resource group module's purpose and design

**EDIT:** After some consideration, I'm going to add this logic to resource group module and repurpose cloud-native-toolkit/terraform-ibm-resource-group#58 to implement this logic. It is somewhat outside the scope of the resource group module but volumes are a special case and we can provide better error information than the IBM Cloud apis in this case (i.e. why the resource group failed to destroy and how to correct it).