CI: build and publish exposed docker package

.github/workflows/docker.yml

@@ -0,0 +1,56 @@
+name: "Publish Docker Image"
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+on:
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+    tags:
+      - "v*" # only publish tagged releases
+
+jobs:
+  build-docker-image:
+    name: "Build Docker Image"
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+
+      - name: Log into ghcr
+        uses: docker/login-action@master
+        with:
+          registry: "${{ env.REGISTRY }}"
+          username: "${{ github.actor }}"
+          password: "${{ secrets.GITHUB_TOKEN }}"
+
+      - name: Build Exposed Docker Image
+        run: nix build .#docker-nix --print-build-logs
+
+      - name: Publish Docker Image
+        run: |
+          #!/usr/bin/env bash
+          set -eu
+
+          docker login "${{ env.REGISTRY }}" --username "${{ github.actor}}" --password "${{ secrets.GITHUB_TOKEN}}"
+
+          # load the built image
+          docker load -i result &&
+
+          # publish the loaded image
+          docker push neovim-flake-nix:latest