Add Terraform CI GitHub actions

* On PR and push to main:
  * runs terraform init, validate, and fmt
  * Ensures .terraform-version is the same as referenced in the workflow
  * Ensures terraform-docs is up to date

Author: Stretch96

.github/workflows/main.yml

@@ -0,0 +1,60 @@
+name: Terraform CI
+
+on:
+  push:
+    branches: main
+  pull_request:
+
+jobs:
+  validate-terraform:
+    name: Validate Terraform
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out code
+      uses: actions/checkout@v1
+
+    - name: Check for terraform version mismatch
+      run: |
+        DOTFILE_VERSION=$(cat .terraform-version)
+        TERRAFORM_IMAGE_REFERENCES=$(grep "uses: docker://hashicorp/terraform" .github/workflows/main.yml | grep -v TERRAFORM_IMAGE_REFERENCES | wc -l | tr -d ' ')
+        if [ "$(grep "docker://hashicorp/terraform:${DOTFILE_VERSION}" .github/workflows/main.yml | wc -l | tr -d ' ')" != "$TERRAFORM_IMAGE_REFERENCES" ]
+        then
+          echo -e "\033[1;31mError: terraform version in .terraform-version file does not match docker://hashicorp/terraform versions in .github/workflows/main.yml"
+          exit 1
+        fi
+
+    - name: Run a Terraform init
+      uses: docker://hashicorp/terraform:1.1.7
+      with:
+        entrypoint: terraform
+        args: init
+
+    - name: Run a Terraform validate
+      uses: docker://hashicorp/terraform:1.1.7
+      with:
+        entrypoint: terraform
+        args: validate
+
+    - name: Run a Terraform format check
+      uses: docker://hashicorp/terraform:1.1.7
+      with:
+        entrypoint: terraform
+        args: fmt -check=true -diff=true
+  validate-terraform-docs:
+    name: Validate Terraform Docs
+    needs: validate-terraform
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+
+      - name: Generate Terraform docs
+        uses: terraform-docs/[email protected]
+        with:
+          working-dir: .
+          config-file: .terraform-docs.yml
+          output-file: README.md
+          output-method: inject
+          fail-on-diff: true