Add missing WORKSPACE files to Docker build image for Bazel version detection

[pudelkoM]

In the current docker builder image bazel(isk) will not pick the Bazel version from the file, because it does not recognize the folder as a Bazel project. This PR fixes this by adding the necessary WORKSPACE and root BUILD files into the container.

Logs from CI run:

Step 31/38 : RUN wget --quiet https://github.com/bazelbuild/bazelisk/releases/download/v${BAZELISK_VERSION}/bazelisk-linux-amd64 &&     mv bazelisk-linux-amd64 /usr/local/bin/bazel &&     chmod +x /usr/local/bin/bazel &&     bazel version
 ---> Running in c25f1a199d1e
2022/03/21 17:11:24 Downloading https://releases.bazel.build/5.0.0/release/bazel-5.0.0-linux-x86_64...
Bazelisk version: v1.8.0
WARNING: Invoking Bazel in batch mode since it is not invoked from within a workspace (below a directory having a WORKSPACE file).
Extracting Bazel installation...
Build label: 5.0.0
Build target: bazel-out/k8-opt/bin/src/main/java/com/google/devtools/build/lib/bazel/BazelServer_deploy.jar
Build time: Wed Jan 19 14:08:54 2022 (1642601334)
Build timestamp: 1642601334
Build timestamp as int: 1642601334

[pudelkoM]

CI fails because of this issue. Here's a successful publish run: https://app.circleci.com/pipelines/github/stratum/stratum/4489/workflows/ed6f401a-f05f-4f50-8eba-1944a761248c/jobs/29320