This patch:
- removes releasing from Travis CI
- sets up a new GH Action that releases @next version from tip-of-tree
Once this GH Action proves to be working, we'll setup a `publish_release.yml`
workflow that will be triggered only by **release** github events
and that will publish released version with `LATEST` tag.
NOTE: this workflow does not actually run publishing - we're doing
`--dry-run` for now to see how it works in
`//utils/publish_all_packages.sh`.
