feat: publish container image (#82)

Use `goreleaser` and `ko` to automatically build and publish container
images in the release workflow. The images are published to
`ghcr.io/apricote/hcloud-upload-image`.

Co-authored-by: Ilja Malachowski <malahovskiy.in@gmail.com>

.github/workflows/release.yaml

@@ -7,11 +7,22 @@ on:
 
 jobs:
   release:
+    permissions:
+      contents: read
+      packages: write
+
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Log in to the Container registry
+        uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Set up Go
         uses: actions/setup-go@v5
         with: