Resources should return an error when an unsupported argument is supplied

[Nicholas Morey]

To make obvious user errors like the one in #89, resources should return an error when an unsupported argument is supplied.

Here's an example of adding an unsupported argument to the google_client_config resource:

│ Error: Unsupported argument
│ 
│   on gcp-gke.tf line 58, in data "google_client_config" "current":
│   58:   test = "my-data"
│ 
│ An argument named "test" is not expected here.

[Jiacheng Xu]

This seems like a common issue from upstream: hashicorp/terraform#33570
that the nested attributes are not validated during conversions.
I verified that other attributes (not nested attributes), for example in cluster resource:

resource "akp_cluster" "example2" {
  instance_id = akp_instance.argocd.id
  name        = "test2"
  unknown = "I am unknown" <- unsupported argument
  namespace   = "akuity"
  labels = {
    label_1 = "example-label"
  }
  annotations = {
    ann_1 = "example-annotation"
  }
  spec = {
    namespace_scoped2 = "true"  <- unsupported argument, it should be namespace_scoped
    description      = "test"
    data = {
      size                  = "small"
      auto_upgrade_disabled = "false"
    }
  }
}

fails with:

│ Error: Unsupported argument
│ 
│   on main.tf line 65, in resource "akp_cluster" "example2":
│   65:   unknown = "I am unknown"
│ 
│ An argument named "unknown" is not expected here.

but because the spec is nested attributes, so it doesn't fail with conversions.