add docker image build workflow

Author: jtriley

.github/workflows/build.yaml

@@ -0,0 +1,59 @@
+name: Build & publish nerc-bootstrap images
+on:
+  release:
+    types: [ published ]
+    tags: [ 'v*.*.*' ]
+  pull_request:
+    branches: [ main ]
+    paths:
+      - ".github/workflows/build.yaml"
+      - "containers/**"
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push-image:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - dockerfile: ./containers/base/Dockerfile
+            image: ghcr.io/nerc-project/nerc-bootstrap/base
+          - dockerfile: ./containers/dhcpd/Dockerfile
+            image: ghcr.io/nerc-project/nerc-bootstrap/dhcpd
+          - dockerfile: ./containers/tftpd/Dockerfile
+            image: ghcr.io/nerc-project/nerc-bootstrap/tftpd
+          - dockerfile: ./containers/httpd/Dockerfile
+            image: ghcr.io/nerc-project/nerc-bootstrap/httpd
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Log in to the Container registry
+        uses: docker/login-action@f054a8b539a109f9f41c372932f1ae047eff08c9
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@98669ae865ea3cffbcbaa878cf57c20bbf1c6c38
+        with:
+          images: ${{ matrix.image }}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@ad44023a93711e3deb337508980b4b5e9bcdc5dc
+        with:
+          context: .
+          file: ${{ matrix.dockerfile }}
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}