Fix build & push Docker image for official tags
Fix build & push Docker image for official tags

CI job `docker` which builds and pushes a cdrouter.py Docker image to
our registry wasn't running for official `vX.Y.Z` tags even though the
CI variable `CI_COMMIT_TAG` was correctly set because of the top-level
`workflow.rules` rules which only allowed running pipelines for
commits to `master`, MR branches, scheduled pipelines and manual
pipelines.  This commit updates `workflow.rules` to also run pipelines
if `CI_COMMIT_TAG` is set to an official `vX.Y.Z` tag.

qacafe/cdrouter.py,qacafe/cdrouter.py