Add an optional provider level label "goog-terraform-provisioned"

[modular-magician]

The intention of this change is to make it easy to identify GCP resources that are managed by Terraform when using other clients like Cloud Console. Overall, this builds on and behaves much the same as provider default labels from #8670, but instead of free form labels it adds a single specific structured label, goog-terraform-provisioned = "true" when enabled. That is:

provider "google" {
  skip_terraform_attribution_label = false
}

Is roughly equivalent to:

provider "google" {
  default_labels = {
    goog-terraform-provisioned = "true"
  }
}

The change is documented in provider_reference.html.markdown. In short, this is a no-op change for users that do not opt in to the feature. For users that do opt in (by setting skip_terraform_attribution_label = false in the provider configuration), there are two modes of operation configured with the optional terraform_attribution_label_addition_strategy field:

• CREATION_ONLY The goog-terraform-provisioned label will only be added to newly created resources. This is the default value.
• PROACTIVE The label will be added to all resources during subsequent terraform apply runs.

Tests are included for a handful of resources, including MMv1, DCL, and handwritten resources.

I'm creating this as a draft PR to gather early feedback (and because as I'm writing this description I thought of some tests changes to make 🤔)

Release Note Template for Downstream PRs (will be copied)

provider: added an optional provider level label `goog-terraform-provisioned` to identify resources that were created by Terraform when viewing/editing these resources in other tools.

Derived from GoogleCloudPlatform/magic-modules#9808

[github-actions]

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