Merge pull request metricq#15 from metricq/chore-migrate-to-ghcr

chore: migrate docker workflow to ghcr.io

hub.docker.com announced their plans to drop the free organizations. While backtracking on those changes,
we still decided to move to ghcr.io, as we are using Github anyways.

.github/workflows/docker.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Prepare
         id: prep
         run: |
-          DOCKER_IMAGE=metricq/metricq-combinator
+          DOCKER_IMAGE=ghcr.io/metricq/metricq-combinator
           VERSION=noop
           if [[ $GITHUB_REF == refs/tags/* ]]; then
             VERSION=${GITHUB_REF#refs/tags/}
@@ -47,15 +47,16 @@ jobs:
         uses: docker/setup-qemu-action@v2
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v2
-      - name: Login to DockerHub
+      - name: Login to Github Container registry
         if: github.event_name != 'pull_request'
         uses: docker/login-action@v2
         with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
       - name: Build and push
         id: docker_build
-        uses: docker/build-push-action@v2
+        uses: docker/build-push-action@v4
         with:
           context: .
           file: ./Dockerfile