Add CI workflow to check for unapproved Go dependency licenses

A task and GitHub Actions workflow are provided here for checking the license types of Go project dependencies.

On every push and pull request that affects relevant files, the CI workflow will check:

- If the dependency licenses cache is up to date
- If any of the project's dependencies have an unapproved license type.

Approval can be based on:

- Universally allowed license type
- Individual dependency

.github/workflows/check-go-dependencies-task.yml

@@ -0,0 +1,109 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/check-go-dependencies-task.md
+name: Check Go Dependencies
+
+env:
+  # See: https://github.com/actions/setup-go/tree/v2#readme
+  GO_VERSION: "1.16"
+
+# See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
+on:
+  push:
+    paths:
+      - ".github/workflows/check-go-dependencies-task.ya?ml"
+      - ".licenses/**"
+      - ".licensed.json"
+      - ".licensed.ya?ml"
+      - "Taskfile.ya?ml"
+      - "**/.gitmodules"
+      - "**/go.mod"
+      - "**/go.sum"
+  pull_request:
+    paths:
+      - ".github/workflows/check-go-dependencies-task.ya?ml"
+      - ".licenses/**"
+      - ".licensed.json"
+      - ".licensed.ya?ml"
+      - "Taskfile.ya?ml"
+      - "**/.gitmodules"
+      - "**/go.mod"
+      - "**/go.sum"
+  workflow_dispatch:
+  repository_dispatch:
+
+jobs:
+  check-cache:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+        with:
+          submodules: recursive
+
+      - name: Install licensed
+        uses: jonabc/setup-licensed@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          version: 3.x
+
+      - name: Install Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ env.GO_VERSION }}
+
+      - name: Install Task
+        uses: arduino/setup-task@v1
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          version: 3.x
+
+      - name: Update dependencies license metadata cache
+        run: task --silent general:cache-dep-licenses
+
+      - name: Check for outdated cache
+        id: diff
+        run: |
+          git add --intent-to-add .
+          if ! git diff --color --exit-code; then
+            echo
+            echo "::error::Dependency license metadata out of sync. See: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/check-go-dependencies-task.md#metadata-cache"
+            exit 1
+          fi
+
+      # Some might find it convenient to have CI generate the cache rather than setting up for it locally
+      - name: Upload cache to workflow artifact
+        if: failure() && steps.diff.outcome == 'failure'
+        uses: actions/upload-artifact@v2
+        with:
+          if-no-files-found: error
+          name: dep-licenses-cache
+          path: .licenses/
+
+  check-deps:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+        with:
+          submodules: recursive
+
+      - name: Install licensed
+        uses: jonabc/setup-licensed@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          version: 3.x
+
+      - name: Install Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ env.GO_VERSION }}
+
+      - name: Install Task
+        uses: arduino/setup-task@v1
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          version: 3.x
+
+      - name: Check for dependencies with unapproved licenses
+        run: task --silent general:check-dep-licenses