The OBS builds run in an environment where no git is installed and
release tarballs assembled manually.
Drop the hard-requirement on git from ci/collect-repo-info.json.
This adds a new utility called ci/collect-repo-info.py to produce a JSON
document that is then baked into the Zeek executable file. Further, when
creating a tarball via `make dist`, put a top-level repo-info.json file
in place that is picked when no .git directory exists.
Closes#1405
