* Add ci/find-current-version.sh to figure out versions of lts and
feature branch based on repository state.
* Do not use ZEEK_IMAGE_REPO for the local images that
are expected to exist.
* Only use IMAGE_NAME/IMAGE_TAG instead of the ARCH and MANIFEST
versions that contained the very same values
* Support and push additional tags
In addition to the lts and feature tags, also push the base version
tags. 5.0 or 5.1 such that someone pulling zeek/zeek:5.0 will get
the most recent available 5.0 patch release.
