Add workflow to use loadbalancer tunnel to juju controller on k8s

This is doing preciely the same scenario that's explained in
https://discourse.charmhub.io/t/a-generic-way-to-communicate-with-a-juju-controller-on-a-k8s-cluster-with-the-juju-terraform-provider/10967

.github/workflows/k8s_tunnel.yml

@@ -0,0 +1,132 @@
+name: Tunnel to Juju controller via load balancer on k8s
+
+on:
+  pull_request:
+    paths-ignore:
+      - "README.md"
+      - "project-docs/**"
+  push:
+    branches:
+      - "main"
+    paths-ignore:
+      - "README.md"
+      - "project-docs/**"
+
+# Testing only needs permissions to read the repository contents.
+permissions:
+  contents: read
+
+jobs:
+  # Ensure project builds before running testing matrix
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v4
+      - run: go build -v .
+
+  # Run acceptance tests in a matrix with Terraform CLI versions
+  add-machine-test:
+    name: Add Machine
+    needs: build
+    runs-on: ubuntu-latest
+    env:
+      ACTIONS_ALLOW_IPV6: false
+    strategy:
+      fail-fast: false
+      matrix:
+        # Only on lxd
+        cloud:
+          - "microk8s"
+        terraform:
+          - "1.5.*"
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v4
+        with:
+          go-version-file: "go.mod"
+          cache: true
+      # set up terraform
+      - uses: hashicorp/setup-terraform@v2
+        with:
+          terraform_version: ${{ matrix.terraform }}
+          terraform_wrapper: false
+      # set up snap, lxd, tox, Juju, bootstrap a controller, etc.
+      - name: Setup operator environment
+        uses: charmed-kubernetes/actions-operator@main
+        with:
+          provider: ${{ matrix.cloud }}
+          juju-channel: 2.9/stable
+      - name: "Set environment to configure provider"
+        # language=bash
+        run: |
+          CONTROLLER=$(juju whoami --format yaml | yq .controller)
+
+          echo "JUJU_CONTROLLER_ADDRESSES=$(juju show-controller | yq .$CONTROLLER.details.api-endpoints | yq -r '. | join(",")')" >> $GITHUB_ENV
+          echo "JUJU_USERNAME=$(juju show-controller | yq .$CONTROLLER.account.user)"  >> $GITHUB_ENV
+          echo "JUJU_PASSWORD=$(cat ~/.local/share/juju/accounts.yaml | yq .controllers.$CONTROLLER.password)"  >> $GITHUB_ENV
+          echo "JUJU_CA_CERT<<EOF" >> $GITHUB_ENV
+          juju show-controller | yq .$CONTROLLER.details.ca-cert >> $GITHUB_ENV
+          echo "EOF" >> $GITHUB_ENV
+      - run: go mod download
+      - run: |
+          # enable ingress and metallb to 
+          sudo microk8s enable ingress
+          sudo microk8s enable metallb
+          
+          # get the service layout
+          microk8s.kubectl get services -n controller-$CONTROLLER controller-service
+          
+          # bring up the load balancer service
+          microk8s.kubectl apply -f - <<EOF
+          apiVersion: v1
+          kind: Service
+          metadata:
+            name: controller-service-lb
+            namespace: controller-k8s29
+          spec:
+            ipFamilies:
+            - IPv4
+            ipFamilyPolicy: SingleStack
+            ports:
+            - name: api-server
+              port: 17070
+              protocol: TCP
+              targetPort: 17070
+            selector:
+              app.kubernetes.io/name: controller
+            sessionAffinity: None
+            type: LoadBalancer
+          EOF
+
+          # get the external IP of the load balancer service 
+          export LB_IP = $(microk8s.kubectl get services -n controller-$CONTROLLER | grep -o 'controller-service-lb.*' | awk '{print $4}')
+          
+          # write a plan using this IP
+          cat <<EOF > ./terraform_config.tf
+          provider "juju" {
+            controller_addresses = \$LB_IP
+            username = \$JUJU_USERNAME
+            password = \$JUJU_PASSWORD
+            ca_certificate = \$JUJU_CA_CERT
+          }
+  
+          resource "juju_model" "testmodel" {
+            name = "test-model"
+          }
+
+          resource "juju_application" "testapp" {
+            name = "ubuntu"
+            model = juju_model.testmodel.name
+
+            charm {
+              name = "ubuntu"
+            }
+          }
+          EOF
+
+          terraform init && terraform plan && terraform apply --auto-approve  
+