Enable Dependabot for automatic updates

Update GitHub Action versions.

Update Go module versions.

.github/dependabot.yml

@@ -0,0 +1,16 @@
+---
+version: 2
+updates:
+- package-ecosystem: gomod
+  directory: /
+  schedule:
+    interval: daily
+  open-pull-requests-limit: 10
+  allow:
+  - dependency-type: "all"
+  target-branch: main
+- package-ecosystem: github-actions
+  directory: /
+  schedule:
+    interval: weekly
+  open-pull-requests-limit: 10

.github/workflows/auto-merge.yml

@@ -0,0 +1,27 @@
+---
+name: Dependabot auto-merge
+
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: ${{ github.actor == 'dependabot[bot]' }}
+    steps:
+    - name: Dependabot metadata
+      id: metadata
+      uses: dependabot/[email protected]
+      with:
+        github-token: "${{ secrets.GITHUB_TOKEN }}"
+
+    - name: Enable auto-merge for Dependabot PRs
+      env:
+        PR_URL: ${{github.event.pull_request.html_url}}
+        GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+      run: |
+        gh pr review --approve "$PR_URL"
+        gh pr merge --auto --merge "$PR_URL"