Switched to Docker's build-publish-action for client's CI

We experienced some problems with `satackey/action-docker-layer-caching`
that caused workflow runners to get out of a disk space. This is related
to the way the action stores layer incrementaly along with the
previously cached ones. See: satackey/action-docker-layer-caching#55

There is also a solution from Docker that we can use for building images
but also on later stage of RFC-18 implementation to publish images to
registires. See: https://github.com/marketplace/actions/build-and-push-docker-images

With the new solution we can also use caching and hopefully it won't
cause problems we had before.

.github/workflows/client.yml

@@ -13,22 +13,39 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: satackey/[email protected]
-        continue-on-error: true # ignore the failure of a step and avoid terminating the job
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Cache Docker layers
+        uses: actions/cache@v2
+        with:
+          path: /tmp/.buildx-cache
+          key: ${{ runner.os }}-buildx-${{ github.ref }}-${{ github.sha }}
+          restore-keys: |
+            ${{ runner.os }}-buildx-${{ github.ref }}-
+            ${{ runner.os }}-buildx-
+
       # TODO: This step was left here intentionally so we can track disk space
       # usage for a while. We were trying to fight problems with out of disk space
       # that happened due to the size of data restored from cache. The cache size
       # was growing linearly with subsequent workflow runs. We want to observe
       # available disk space for `/`. Fresh execution starts with 20 GB, we expect
       # to have no less than 15 GB after the cache is restored.
       - run: sudo df -h
-      - name: Run Docker build
-        run: |
-          docker build \
-            --target gobuild \
-            --tag go-build-env .
-          docker build \
-            --tag keep-client . 
+
+      - name: Build Docker Build Image
+        uses: docker/build-push-action@v2
+        with:
+          target: gobuild
+          tags: go-build-env
+          build-args: |
+            REVISION=${{ github.sha }}
+          # VERSION= ? TODO: Configure version, sample: 1.7.6
+          load: true # load image to local registry to use it in next steps
+          cache-from: type=local,src=/tmp/.buildx-cache
+          cache-to: type=local,dest=/tmp/.buildx-cache
+
       - name: Create test results directory
         run: |
           mkdir test-results
@@ -47,3 +64,15 @@ jobs:
           files:  ./test-results/unit-tests.xml
           check_name: Go Test Results # name under which test results will be presented in GitHub (optional)
           comment_on_pr: false # turns off commenting on Pull Requests
+
+      # This step is executed after the tests as we want to configure it eventually
+      # as image publication step.
+      - name: Build Docker Runtime Image
+        uses: docker/build-push-action@v2
+        with:
+          tags: keep-client
+          labels: |
+            revision=${{ github.sha }}
+          # TODO: Check branch name and publish to a registry accordingly to the
+          # environment.
+          # push: true # publish to registry