add GitHub Pages for post-mortems

- Index page listing all incident reports
- GHA workflow deploys post-mortems/ on push
- Available at viktorbarzin.github.io/infra/

.github/workflows/deploy-postmortems.yml

@@ -0,0 +1,32 @@
+name: Deploy Post-Mortems to GitHub Pages
+
+on:
+  push:
+    branches: [master]
+    paths:
+      - 'post-mortems/**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/configure-pages@v5
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: post-mortems
+      - id: deployment
+        uses: actions/deploy-pages@v4