Add Resource attribute for "Internal Cluster Name"

[knikolla]

We currently use an internal cluster name that may be different from what is presented to users in the ColdFront UI (the Resource name itself)

Create a Resource attribute of type string named Internal Cluster Name to allow storing this for each resource.

• Add to register_cloud_attributes
• Implement in calculate_storage_gb_hours to fetch outage for each specific cluster using the internal cluster name.