docs(k8s): update terraform-gke example for Bonsai (#4000)

* Generate kubeconfig for GKE cluster

In order to "one-shot" deploy the example a GKE cluster and our demo
services, we need a kubeconfig. Because of
#3475, a kubeconfig managed by
Garden should be generated with elevated privileges.

* Set hardcoded values to variables

To improve comprehension and expose the values a user should set for a
project at the top of the file, we set the hardcoded values of the
Garden project file to variables.

* Convert 0.12 modules to 0.13

* Specify Terraform one-shot deployments in docs

The README previously assumed a cluster ready to work with. We change
the instructions to assume no pre-existing cluster.

* Simplify and atomize terraform

Previously the GKE example was an all-in-one terraform file. I've chosen
to make use of battle-tested GKE modules and split the terraform for
easy comprehension.

examples/terraform-gke/README.md

@@ -35,28 +35,18 @@ The Terraform stack needs some input values from you. You can provide those in a
 
 ```tfvars
 # terraform.tfvars
-gcp_region     = "europe-west1"°
-gcp_project_id = "my-test-project"
+region     = "europe-west1"°
+project_id = "my-test-project"
 ```
 
 **B)** Configure the variables directly in the project `garden.yml` (see the `terraform` provider section).
 
-### Step 4 - Initialize the cluster
+### Step 4 - Deploy your stack
 
-Install the cluster-wide services Garden needs by running:
+Finally, build and deploy your GKE cluster and services to the new cluster:
 
 ```sh
-garden plugins kubernetes cluster-init
-```
-
-This will take a while because the cluster needs to be provisioned, and some services installed when it's ready.
-
-### Step 5 - Deploy your services
-
-Finally, to build and deploy your services to your new GKE cluster, run:
-
-```sh
-garden deploy
+garden deploy -l2 #the -l2 flag is optional, but recommended to observe the progress of the Terraform deployment
 ```
 
 And that's it!

examples/terraform-gke/backend/garden.yml

@@ -1,14 +1,19 @@
-kind: Module
+kind: Build
 name: backend
+type: container
+
+---
+
+kind: Deploy
+name: backend
+build: backend
 description: Backend service container
 type: container
-services:
-  - name: backend
-    ports:
-      - name: http
-        containerPort: 8080
-        # Maps service:80 -> container:8080
-        servicePort: 80
-    ingresses:
-      - path: /hello-backend
-        port: http
+spec:
+  ports:
+    - name: http
+      containerPort: 8080
+      servicePort: 80
+  ingresses:
+    - path: /hello-backend
+      port: http

examples/terraform-gke/frontend/garden.yml

@@ -1,27 +1,43 @@
-kind: Module
+kind: Build
 name: frontend
+type: container
+
+---
+kind: Deploy
+name: frontend
+build: frontend
 description: Frontend service container
 type: container
-services:
-  - name: frontend
-    ports:
-      - name: http
-        containerPort: 8080
-    healthCheck:
-      httpGet:
-        path: /hello-frontend
-        port: http
-    ingresses:
-      - path: /hello-frontend
-        port: http
-      - path: /call-backend
-        port: http
-    dependencies:
-      - backend
-tests:
-  - name: unit
-    args: [npm, test]
-  - name: integ
-    args: [npm, run, integ]
-    dependencies:
-      - frontend
+spec:
+  ports:
+    - name: http
+      containerPort: 8080
+  healthCheck:
+    httpGet:
+      path: /hello-frontend
+      port: http
+  ingresses:
+    - path: /hello-frontend
+      port: http
+    - path: /call-backend
+      port: http
+dependencies:
+  - deploy.backend
+
+---
+kind: Test
+name: frontend-unit
+build: frontend
+type: container
+spec:
+  args: [npm, test]
+
+---
+kind: Test
+name: frontend-integ
+build: frontend
+type: container
+spec:
+  args: [npm, run, integ]
+dependencies:
+  - deploy.backend

examples/terraform-gke/garden.yml

@@ -1,25 +1,45 @@
 kind: Project
 name: terraform-gke
+
+environments:
+  - name: dev
+    defaultNamespace: ${project.name}-${variables.userId}
+  - name: prod
+    defaultNamespace: ${project.name}
+    production: true
+
+variables:
+  # change these values to your own
+  username: worldofgeese
+  gcpProjectId: devrel-348008
+  gcpRegion: europe-north1
+  registryHostname: docker.io
+  registryNamespace: worldofgeese
+  terraformInitRoot: "./terraform/"
+  userId: ${local.username}
 providers:
   - name: terraform
-    # This must be set to indicate that there is a stack in the project root.
-    initRoot: "."
+    # This must be set to indicate that there is a stack in the terraform project folder.
+    initRoot: "${var.terraformInitRoot}"
+    autoApply: true
     # You can either uncomment and replace these with your own values, or provide the values in a
     # terraform.tfvars file in the project root.
     # variables:
     #   gcp_project_id: garden-gke-tf-${var.userId}
     #   gcp_region: europe-west1
+    allowDestroy: true
+    # You can either uncomment and replace these with your own values, or provide the values in a
+    # terraform.tfvars file in the project root.
+    variables:
+      project_id: ${var.gcpProjectId}
+      region: ${var.gcpRegion}
+
   - name: kubernetes
-    kubeconfig: ${providers.terraform.outputs.kubeconfig_path}
-    context: gke
-    defaultHostname: terraform-gke-${var.userId}.dev-2.sys.garden
-    buildMode: kaniko
+    kubeconfig: ${var.terraformInitRoot}/${providers.terraform.outputs.kubeconfig_path}
+    context: ${providers.terraform.outputs.cluster_name}
+    # any hostname that points to your cluster's ingress controller
+    defaultHostname: ${var.userId}-gke.dev-1.sys.garden
     # Replace the below values as appropriate
     deploymentRegistry:
-      hostname: eu.gcr.io    # <- set this according to the region your cluster runs in
-      namespace: garden-ci   # <- set this to the project ID of the target cluster
-    imagePullSecrets:
-      # Make sure this matches the name and namespace of the imagePullSecret you've created
-      # to authenticate with your registry (if needed)
-      - name: gcr-config
-        namespace: default
+      hostname: ${variables.registryHostname}
+      namespace: ${variables.registryNamespace}