Add Terraform fmt GitHub Action and dependabot config

* Run terraform fmt on pull requests and merge to main
* Show workflow status in README
* Add dependabot.yaml to keep GitHub Actions updated

.github/dependabot.yaml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+- package-ecosystem: "github-actions"
+  directory: "/"
+  schedule:
+    interval: "daily"

.github/workflows/test.yaml

@@ -0,0 +1,21 @@
+name: test
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+jobs:
+  terraform:
+    name: fmt
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v3
+
+      - name: terraform
+        uses: hashicorp/setup-terraform@v2
+        with:
+          terraform_version: 1.2.5
+
+      - name: fmt
+        run: terraform fmt -check -diff -recursive