add publish devcontainer workflow

Author: smithclay

.github/workflows/publish-devcontainer.yml

@@ -0,0 +1,55 @@
+name: Publish Devcontainer to GHCR
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - '.devcontainer/Dockerfile'
+      - '.github/workflows/publish-devcontainer.yml'
+  workflow_dispatch:
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}/devcontainer
+
+jobs:
+  publish-devcontainer:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      
+      - name: Log in to Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=sha,prefix={{branch}}-
+            type=raw,value=latest,enable={{is_default_branch}}
+      
+      - name: Build and push devcontainer image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: .devcontainer/Dockerfile
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max