added sonic base image workflow (#251)

Author: ostempel

.github/workflows/base-image.yaml

@@ -0,0 +1,37 @@
+---
+name: Build sonic base image
+on: workflow_dispatch
+
+env:
+  REGISTRY: ghcr.io
+
+jobs:
+  build-mini-lab-sonic-base-image:
+    name: build mini-lab-sonic base image
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Log in to the container registry
+      uses: docker/login-action@v3
+      with:
+        registry: ${{ env.REGISTRY }}
+        username: ${{ secrets.DOCKER_REGISTRY_USER }}
+        password: ${{ secrets.DOCKER_REGISTRY_TOKEN }}
+
+    - name: Checkout
+      uses: actions/checkout@v4
+
+    - name: Make tag
+      run: |
+        [ "${GITHUB_EVENT_NAME}" == 'workflow_dispatch' ] && echo "tag=${GITHUB_HEAD_REF##*/}" >> $GITHUB_ENV 
+
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+
+    - name: Build and push mini-lab-sonic container
+      uses: docker/build-push-action@v6
+      with:
+        push: true
+        sbom: true
+        file: images/sonic/base/Dockerfile
+        tags: ${{ env.REGISTRY }}/metal-stack/mini-lab-sonic-base:${{ env.tag }}