Add proper stamping

Pushing the container images currently fails, because we haven't
included the shell script that is responsible for stamping.

Author: EdSchouten

.bazelrc

@@ -0,0 +1 @@
+run --workspace_status_command="bash tools/workspace-status.sh"

tools/workspace-status.sh

@@ -0,0 +1,6 @@
+#!/bin/sh -e
+
+if test "${GITHUB_ACTIONS}" = "true"; then
+  echo "BUILD_SCM_REVISION $(git rev-parse --short HEAD)"
+  echo "BUILD_SCM_TIMESTAMP $(TZ=UTC date --date "@$(git show -s --format=%ct HEAD)" +%Y%m%dT%H%M%SZ)"
+fi