Add a GH action for deploying on PR merge

.github/workflows/firebase-hosting-merge.yml

@@ -0,0 +1,28 @@
+# This file was auto-generated by the Firebase CLI
+# https://github.com/firebase/firebase-tools
+
+name: Deploy to Firebase Hosting on merge
+'on':
+  push:
+    branches:
+      - master
+jobs:
+  build_and_deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+      - name: Set up hugo
+        uses: peaceiris/actions-hugo@v2
+        with:
+          hugo-version: 'latest'
+      - name: Run hugo
+        run: hugo
+      - name: Deploy
+        uses: FirebaseExtended/action-hosting-deploy@v0
+        with:
+          repoToken: '${{ secrets.GITHUB_TOKEN }}'
+          firebaseServiceAccount: '${{ secrets.FIREBASE_SERVICE_ACCOUNT_BENTSUKUN_CH }}'
+          channelId: live
+          projectId: bentsukun-ch