fix: Allow nested Terraform resources (#1093)

This fixes the dependency tree by adding recursion. It
now finds indirect connections and associates it with
an agent.

An example is attached which surfaced this issue.

examples/gcp-vm-container/README.md

@@ -0,0 +1,5 @@
+---
+name: Develop in a container on a Google Cloud VM
+description: Get started with Linux development on Google Cloud.
+tags: [cloud, google, container]
+---

examples/gcp-vm-container/main.tf

@@ -0,0 +1,103 @@
+terraform {
+  required_providers {
+    coder = {
+      source  = "coder/coder"
+      version = "~> 0.3.1"
+    }
+    google = {
+      source  = "hashicorp/google"
+      version = "~> 4.15"
+    }
+  }
+}
+
+variable "service_account" {
+  description = <<EOF
+Coder requires a Google Cloud Service Account to provision workspaces.
+
+1. Create a service account:
+   https://console.cloud.google.com/projectselector/iam-admin/serviceaccounts/create
+2. Add the roles:
+   - Compute Admin
+   - Service Account User
+3. Click on the created key, and navigate to the "Keys" tab.
+4. Click "Add key", then "Create new key".
+5. Generate a JSON private key, and paste the contents below.
+EOF
+  sensitive   = true
+}
+
+variable "zone" {
+  description = "What region should your workspace live in?"
+  default     = "us-central1-a"
+  validation {
+    condition     = contains(["northamerica-northeast1-a", "us-central1-a", "us-west2-c", "europe-west4-b", "southamerica-east1-a"], var.zone)
+    error_message = "Invalid zone!"
+  }
+}
+
+provider "google" {
+  zone        = var.zone
+  credentials = var.service_account
+  project     = jsondecode(var.service_account).project_id
+}
+
+data "google_compute_default_service_account" "default" {
+}
+
+data "coder_workspace" "me" {
+}
+
+resource "coder_agent" "dev" {
+  auth = "google-instance-identity"
+  arch = "amd64"
+  os   = "linux"
+}
+
+module "gce-container" {
+  source  = "terraform-google-modules/container-vm/google"
+  version = "3.0.0"
+
+  container = {
+    image   = "mcr.microsoft.com/vscode/devcontainers/go:1"
+    command = ["sh"]
+    args    = ["-c", coder_agent.dev.init_script]
+    securityContext = {
+      privileged : true
+    }
+  }
+}
+
+resource "google_compute_instance" "dev" {
+  zone         = var.zone
+  count        = data.coder_workspace.me.start_count
+  name         = "coder-${data.coder_workspace.me.owner}-${data.coder_workspace.me.name}"
+  machine_type = "e2-medium"
+  network_interface {
+    network = "default"
+    access_config {
+      // Ephemeral public IP
+    }
+  }
+  boot_disk {
+    initialize_params {
+      image = module.gce-container.source_image
+    }
+  }
+  service_account {
+    email  = data.google_compute_default_service_account.default.email
+    scopes = ["cloud-platform"]
+  }
+  metadata = {
+    "gce-container-declaration" = module.gce-container.metadata_value
+  }
+  labels = {
+    container-vm = module.gce-container.vm_container_label
+  }
+}
+
+resource "coder_agent_instance" "dev" {
+  count       = data.coder_workspace.me.start_count
+  agent_id    = coder_agent.dev.id
+  instance_id = google_compute_instance.dev[0].instance_id
+}