gha: Add workflow to update major tag

Author: peaceiris

.github/workflows/update-major-tag.yml

@@ -0,0 +1,24 @@
+name: Update major tag
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  update:
+    runs-on: ubuntu-18.04
+    steps:
+
+    - uses: actions/checkout@v1
+
+    - name: Update major tag
+      if: github.event.release.prerelease == false
+      run: |
+        git config user.name "${GITHUB_ACTOR}"
+        git config user.email "${GITHUB_ACTOR}@users.noreply.github.com"
+        git remote set-url origin "https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/${GITHUB_REPOSITORY}.git"
+        export TAG_NAME="${GITHUB_REF##refs/tags/}"
+        export TAG_MAJOR="${TAG_NAME%%.*}"
+        git tag "${TAG_MAJOR}" || git tag -d "${TAG_MAJOR}" ; git push origin ":refs/tags/${TAG_MAJOR}"
+        git tag "${TAG_MAJOR}" || true
+        git push --tags origin