Add GitHub Actions workflow for Docker image build and testing

Author: Donaim

.github/workflows/main.yml

@@ -1,2 +1,31 @@
+name: main tests
 
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
 
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+          fetch-depth: 0
+      
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      
+      - name: Build Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./bblab.dockerfile
+          target: bblab-site
+          push: false
+          tags: cfe-lab/bblab-site:${{ github.sha }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max