artifactregistry: add google_artifact_registry_project_config for platform logs

[modular-magician]

Adds a new resource google_artifact_registry_project_config that manages the Artifact Registry project config — a project+location singleton — exposing its nested platformLogsConfig so platform logs can be enabled/disabled and given a severity threshold via Terraform.

Modeled on the sibling google_artifact_registry_vpcsc_config: the config always exists per location, so create/update are PATCH (with a hardcoded updateMask=platformLogsConfig), and the resource is acquire-and-update with a state-only delete (exclude_delete).

Resolves hashicorp/terraform-provider-google#27747

Example:

resource "google_artifact_registry_project_config" "config" {
  location = "us-central1"
  platform_logs_config {
    logging_state  = "ENABLED"
    severity_level = "INFO"
  }
}

`google_artifact_registry_project_config`

Derived from GoogleCloudPlatform/magic-modules#18020