ci: add docker image workflow

.github/workflows/docker.yml

@@ -0,0 +1,14 @@
+name: Docker Image CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build the Docker image
+      run: docker build . --file Dockerfile --tag VERT-sh/vert:$(date +%s)