Add GitHub Actions workflow.

Author: rakino

.github/workflows/build.yml

@@ -0,0 +1,41 @@
+name: Build and publish Docker image
+
+on:
+  push:
+    branches:
+      - trunk
+  workflow_dispatch:
+
+permissions:
+  packages: write
+
+jobs:
+  push_to_registry:
+    name: Push Docker image to GitHub Container registry
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and Push to Container registry
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: linux/amd64
+          push: true
+          tags: ghcr.io/rakino/misskey:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max