[WIP] Add initial CI workflow

This commit adds an initial GitHub Actions CI workflow for building and
pushing the Docker image.

Signed-off-by: Stephanos Ioannidis <[email protected]>

.github/workflows/ci.yml

@@ -0,0 +1,55 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+    tags: [ 'v*' ]
+  pull_request:
+    branches: [ main ]
+
+permissions:
+  packages: write
+
+concurrency:
+  group: ${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-22.04-4c
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+
+    - name: Generate metadata
+      id: meta
+      uses: docker/metadata-action@v4
+      with:
+        images: |
+          ghcr.io/zephyrproject-rtos/ci-repo-cache
+
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v3
+
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+
+    - name: Login to GitHub Container Registry
+      if: ${{ github.event_name != 'pull_request' }}
+      uses: docker/login-action@v3
+      with:
+        registry: ghcr.io
+        username: ${{ github.repository_owner }}
+        password: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Build and push Docker image
+      uses: docker/build-push-action@v5
+      with:
+        context: .
+        file: Dockerfile
+        platforms: linux/amd64,linux/arm64
+        push: ${{ github.event_name != 'pull_request' }}
+        tags: ${{ steps.meta.outputs.tags }}
+        labels: ${{ steps.meta.outputs.labels }}