.github: add workflow to build docker image

Author: willnorris

.github/workflows/docker.yml

@@ -0,0 +1,59 @@
+name: Docker
+
+on:
+  push:
+    branches: [ 'main' ]
+    tags: [ 'v*' ]
+  pull_request:
+    branches: [ 'main' ]
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push-image:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+      id-token: write
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Setup Docker buildx
+      uses: docker/setup-buildx-action@8c0edbc76e98fa90f69d9a2c020dcb50019dc325 # v2.2.1
+
+    - name: Log into registry ${{ env.REGISTRY }}
+      uses: docker/login-action@f4ef78c080cd8ba55a85445d5b36e214a81df20a # v2.1.0
+      if: github.event_name != 'pull_request'
+      with:
+        registry: ${{ env.REGISTRY }}
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Extract Docker metadata
+      id: meta
+      uses: docker/metadata-action@57396166ad8aefe6098280995947635806a0e6ea # v4.1.1
+      with:
+        images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+    - name: Build and push Docker image
+      id: build-and-push
+      uses: docker/build-push-action@c56af957549030174b10d6867f20e78cfd7debc5 # v3.2.0
+      with:
+        context: .
+        push: ${{ github.event_name != 'pull_request' }}
+        tags: ${{ steps.meta.outputs.tags }}
+        labels: ${{ steps.meta.outputs.labels }}
+
+    # Sign the Docker image
+    - name: Install cosign
+      if: github.event_name != 'pull_request'
+      uses: sigstore/cosign-installer@9becc617647dfa20ae7b1151972e9b3a2c338a2b #v2.8.1
+    - name: Sign the published Docker image
+      if: github.event_name != 'pull_request'
+      env:
+        COSIGN_EXPERIMENTAL: "true"
+      run: cosign sign ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}@${{ steps.build-and-push.outputs.digest }}