ci: create builder for building Docker containers with buildx

Apparently, the default builder does not allow using a cache when
building images.

I think that this creates the builder using the `docker-container`
driver.

Some resources:
- https://docs.docker.com/build/ci/github-actions/configure-builder/
- https://docs.docker.com/build/ci/github-actions/cache/
- https://docs.docker.com/build/drivers/docker-container/
- https://stackoverflow.com/questions/61491484/how-to-cache-docker-compose-build-inside-github-action
- https://github.com/orgs/community/discussions/25728
- https://github.com/docker/setup-buildx-action

Related to #83

.github/workflows/default.yml

@@ -82,6 +82,8 @@ jobs:
         with:
           # We need to fetch all branches and commits so that Nx affected has a base to compare against.
           fetch-depth: 0
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
       - uses: nrwl/nx-set-shas@v3
         with:
           main-branch-name: 'master'