Reuse of cloud_provider for other fields

[bryan-bar]

Is your feature request related to a problem? Please describe.
We are defining the cloud_provider and then having to specify it in again under other schema inputs and think the provider should handle this instead.
For example:

instance_type = "azure:Standard_D2s_v3"
storage {
    volume_type       = "azurepremiumstorage"
    volume_properties = "P1"
    size              = "4 Gi"
  }
cloud_provider        = "azure"
region                = "eastus2"

Here we define azure:Standard_D2s_v3 and azurepremiumstorage

instance_type = "aws:c5.large"
storage {
    volume_type       = "gp3"
    volume_properties = "gp3"
    size              = "4 Gi"
  }
cloud_provider        = "aws"
region                = "us-east-1"

Here we define aws:c5.large

Describe the solution you'd like
I think we should remove the cloud provider prefixes or hide it from the user and reuse cloud_provider.

Describe alternatives you've considered
With edb-terraform, we use jinja for templating and so we could hide some of this from the user with mappings and/or string concatenation.